Methods and apparatuses for casting polymer products

ABSTRACT

An example system for molding a photocurable material into a planar object includes a first mold structure having a first mold surface, a second mold structure having a second mold surface, and one or more protrusions disposed along at least one of the first mold surface or the second mold surface. During operation, the system is configured to position the first and second mold structures such that the first and second mold surfaces face each other with the one or more protrusions contacting the opposite mold surface, and a volume having a total thickness variation (TTV) of 500 nm or less is defined between the first and second mold surfaces. The system is further configured to receive the photocurable material in the volume, and direct radiation at the one or more wavelengths into the volume.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority from U.S. Provisional Application Ser.No. 62/573,479, filed on Oct. 17, 2017, and U.S. Provisional ApplicationSer. No. 62/746,426, filed on Oct. 16, 2018, which are incorporatedherein by reference in their entirety.

TECHNICAL FIELD

This disclosure relates to optical polymer films and methods forproducing the same.

BACKGROUND

Optical imaging systems, such as wearable imaging headsets, can includeone or more eyepieces that present projected images to a user. Eyepiecescan be constructed using thin layers of one or more highly refractivematerials. As examples, eyepieces can be constructed from one or morelayers of highly refractive glass, silicon, metal, or polymersubstrates.

In some cases, an eyepiece can be patterned (e.g., with one or morelight diffractive nanostructures), such that it projects an imageaccording to a particular focal depth. For an example, to a user viewinga patterned eyepiece, the projected image can appear to be a particulardistance away from the user.

Further, multiple eyepieces can be used in conjunction to project asimulated three-dimensional image. For example, multiple eyepieces—eachhaving a different pattern—can be layered one atop another, and eacheyepiece can project a different depth layer of a volumetric image.Thus, the eyepieces can collectively present the volumetric image to theuser across three-dimensions. This can be useful, for example, inpresenting the user with a “virtual reality” environment.

To improve the quality of a projected image, an eyepiece can beconstructed such that unintended variations in the eyepiece areeliminated, or otherwise reduced. For example, an eyepiece can beconstructed such that it does not exhibit any wrinkles, uneventhicknesses, or other physical distortions that might negatively affectthe performance of the eyepiece.

SUMMARY

System and techniques for producing polymer films are described herein.One or more of the described implementations can be used to producepolymer film in a highly precise, controlled, and reproducible manner.The resulting polymer films can be used in a variety ofvariation-sensitive applications in which extremely tight tolerances onfilm dimensions are desired. For instance, the polymer films can be usedin optical applications (e.g., as a part of eyepieces in an opticalimaging system) in which material homogeneity and dimensionalconstraints are on the order of optical wavelengths or smaller.

In some cases, polymer films can be produced by enclosing a photocurablematerial (e.g., a photopolymer or light-activated resin that hardenswhen exposed to light) between two molds, and curing the material (e.g.,by exposing the material to light and/or heat).

However, during the casting and curing process, various factors caninterfere with the shape of the resulting film, causing it to becomedistorted from its intended shape. For example, during the castingprocess, particular matter may be unintentionally entrapped between twomold surfaces, and interfere with the interaction between them. As aresult, this may cause the relative orientation of the mold surfaces todeviate from the intended orientation (e.g., such that the mold surfacesare no longer parallel to each other), resulting in a film that deviatesfrom its intended shape. For instance, the resulting film may have anuneven thickness across its extent. As another example, during thecuring process, the material may expand or contract within the molds. Asa result, the film may become distorted (e.g., wrinkled, stretched, orcompressed). Accordingly, the film may be less suitable for use invariation-sensitive applications.

To improve the quality and consistency of the film, the position of thetwo molds can be precisely controlled, such that the molds are keptparallel to each other immediately prior to and/or during the curing ofthe material. In some cases, this can be achieved, at least in part,through the use of physical registration features positioned on one ormore of the molds. As an example, molds can include one or more spacerstructures (e.g., protrusions or gaskets) that project from one or moresurfaces of the mold and towards an opposing mold. As another example,molds can include one or more recesses (e.g., slots or grooves) definedalong one or more surfaces of the mold that accept one or more spacerstructures from an opposing mold. The spacer structures and/or recessescan be used to physically align the molds, such that the relativeorientation of the mold surfaces are less likely to deviate from theintended orientation. For example, the spacer structures and/or recessescan be used to maintain a parallel orientation between two molds. As aresult, the photocurable material has a more even thickness, and is lesslikely to become distorted during the curing process.

In some cases, a “singulation” process can be performed to separate apolymer film into multiple different products (e.g., by cutting thepolymer film one or more times to obtain separate products havingparticular sizes and shapes).

However, a singulation process may introduce undesirable variations inthe polymer film, and render the resulting products less suitable foruse in variation-sensitive environments. For example, high power lasersare often used to cut certain types of optical materials, such asglass-based substrates (e.g., during the production of glass-basedeyepieces). However, the use of lasers may be less suitable for cuttingrelatively softer materials with lower melting points, such as polymerfilm. For instance, lasers produce high temperatures locally onto thepolymer film, which may result in localized physical and/or chemicaldamage to the polymer film (e.g., permanent deposition of fumes and/ordebris into the polymer film). Further, the use of lasers may impart anundesirable odor in the polymer film (e.g., due to the oxidation ofsulfur/thiol groups in the polymer film).

As an alternative, polymer products can be produced without performing asingulation process. For example, two molds can be configured such that,when the molds are brought together, they define an enclosed regioncorresponding to the size and shape of single polymer product. Duringthe production process, a photocurable material is enclosed between thetwo molds, and the material is cured to form a polymer film. Aftercuring, the polymer film is extracted from the molds, resulting in asingle polymer product having a particular predefined size and shape.This polymer product can be subsequently used in other manufacturingprocesses (e.g., incorporated into an apparatus, such as a headset)without the need for an additional singulation step. Accordingly, thepolymer product is less likely to have physical and/or chemical damage(e.g., compared to a polymer product formed through singulation of alarger polymer film), and can be more suitable for use invariation-sensitive environments.

Further, in some cases, a film can become distorted due to the build upof internal stresses within during the polymerization process. Forinstance, as a photocurable material is cured, monomers of thephotocurable material polymerize into longer and heavier chains.Correspondingly, the photocurable material reduces in volume (e.g.,experiences “shrinkage”) as the polymer chains physically move together.This results in a build up to internal stresses inside of thephotocurable material (e.g., stresses resulting from an impedance topolymer chain mobility), and a storage of strain energy within thephotocurable material. When the cured film is extracted from the mold,the strain energy is released resulting in thinning of the film. Thefilm can thin differently depending on the spatial distribution of theinternal stresses. Thus, films may exhibit variations from film to film,depending on the particular spatial distribution of internal stressesthat were introduced during the polymerization process. Accordingly, theconsistency of a film can be improved by regulating the distribution ofstress within the film during the casting process. Example systems andtechniques for regulating stress in a film are described herein.

In an aspect, a system for molding a photocurable material into a planarobject includes a first mold structure including a first mold surface.The first mold surface includes a planar area extending in a firstplane. The system also includes a second mold structure including asecond mold surface including a planar area extending in a second plane.At the corresponding planar area, at least one of the first moldstructure or the second mold structure is substantially transparent toradiation at one or more wavelengths suitable for photocuring thephotocurable material. The system also includes one or more protrusionsdisposed along at least one of the first mold surface or the second moldsurface. During operation, the system is configured to position thefirst and second mold structures such that the first and second moldsurfaces face each other with the one or more protrusions contacting theopposite mold surface, the first plane is parallel to the second plane,and a volume having a total thickness variation (TTV) of 500 nm or lessis defined between the first and second mold surfaces adjacent thecorresponding planar areas. During operation, the system is alsoconfigured to receive the photocurable material in the volume, anddirect radiation at the one or more wavelengths into the volume.

Implementations of this aspect can include one or more of the followingfeatures.

In some implementations, each of the first mold structure and the secondmold structure can have a thickness greater than 1 mm.

In some implementations, each of the first mold structure and the secondmold structure can have a thickness between 1 mm and 50 mm.

In some implementations, each of the first mold structure and the secondmold structure can have a diameter greater than 3 inches.

In some implementations, the system can further include one or morerecesses defined along at least one of the first mold surface or thesecond mold surface.

In some implementations, during operation, at least some of the one ormore protrusions can be in alignment with the at least some of the oneor more recesses, such that when the system positions the first andsecond mold structures so that the first and second mold surfaces faceeach other with the one or more protrusions contacting the oppositesurface, at least some of the one or more protrusions insert, at leastpartially, into at least some of the recesses.

In some implementations, at least some of the one or more protrusionscan be disposed along a periphery of the first mold surface.

In some implementations, at least some of the one or more protrusionscan be disposed along an interior of the first mold surface.

In some implementations, at least some of the one or more recessesprotrusions can be disposed along a periphery of the second moldsurface.

In some implementations, at least some of the one or more recessesprotrusions can be disposed along an interior of the second moldsurface.

In some implementations, at least some of the one or more protrusionscan have a substantially rectangular cross-section.

In some implementations, at least some of the one or more protrusionshaving the substantially rectangular cross-section can further include arespective substantially hemispherical distal end.

In some implementations, at least some of the one or more protrusionshaving the substantially rectangular cross-section can further includeone or more rounded corners.

In some implementations, at least some of the one or more protrusionscan have a substantially triangular cross-section.

In some implementations, at least some of the one or more protrusionshaving the substantially triangular cross-section can further includeone or more rounded corners.

In some implementations, at least some of the one or more recesses canhave a substantially rectangular cross-section.

In some implementations, at least some of the one or more recesseshaving the substantially rectangular cross-section can further includeone or more rounded corners.

In some implementations, at least some of the one or more recesses canhave a substantially triangular cross-section.

In some implementations, at least some of the one or more recesseshaving the substantially triangular cross-section can further includeone or more rounded corners.

In some implementations, at least some of the one or more protrusionscan be integral with least one of the first mold surface or the secondmold surface.

In some implementations, at least some of the one or more protrusionscan be detachable from the first mold surface or the second moldsurface.

In some implementations, the system can further include a light assemblyconfigured to emit one or more wavelengths of radiation suitable forphotocuring the photocurable material.

In some implementations, the first and second mold surfaces can bepolished surfaces.

In some implementations, during operation, the system can be configuredto position the first and second mold structures such that the volumedefined between the first and second mold surfaces adjacent thecorresponding planar areas has a total thickness variation (TTV) of 100nm or less.

In some implementations, each of the one or more protrusions can have atotal thickness variation of 100 nm or less.

In some implementations, each of the one or more recesses can have atotal thickness variation of 100 nm or less.

In some implementations, during operation, the system can be configuredto position the first and second mold structures such that the volumedefined between the first and second mold surfaces adjacent thecorresponding planar areas has a thickness between 20 μm and 2 mm.

In some implementations, during operation, the system can be configuredto direct heat into the volume. The system can be configured to directheat into the volume through the first mold surface. The system can beconfigured to direct heat into the volume through the second moldsurface.

In some implementations, during operation, the system can be configuredto direct the one or more wavelengths of radiation into the volumethrough the first mold surface.

In some implementations, during operation, the system can be configuredto direct the one or more wavelengths of radiation into the volumethrough the second mold surface.

In another aspect, a method of forming a waveguide part having apredetermined shape includes providing a first mold portion having afirst surface including a discrete, continuous first area correspondingto the predetermined shape of the waveguide part. The first area isbounded by an edge region having a different surface chemistry and/orsurface structure than the first area. The method also includesproviding a second mold portion having a second surface including adiscrete, continuous second area corresponding to the predeterminedshape of the waveguide part. The second area is bounded by an edgeregion having a different surface chemistry and/or surface structurethan the second area. The method also includes dispensing a meteredamount of a photocurable material into a space adjacent the first areaof the first mold portion, and arranging the first and second surfacesopposite each other with the first and second areas being registeredwith respect to each other. The method also includes adjusting arelative separation between the first surface and the second surface sothat the photocurable material fills a space between first and secondareas of the first and second surfaces, respectively, having thepredetermined shape. The different surface chemistry and/or surfacestructure between the first and second areas and their correspondingedge regions prevent flow of the photocurable material beyond the edgeregions. The method also includes irradiating the photocurable materialin the space with radiation suitable for photocuring the photocurablematerial to form a cured film in the shape of the waveguide part, andseparating the cured film from the first and second mold portions toprovide the waveguide part.

Implementations of this aspect can include one or more of the followingfeatures.

In some implementations, the metered amount of photocurable material canbe dispensed at a plurality of discrete locations in the space adjacentthe first area of the first mold portion.

In some implementations, the metered amount of photocurable material canbe dispensed according to an asymmetric pattern in the space adjacentthe first area of the first mold portion.

In some implementations, the metered amount of photocurable material canbe dispensed at a periphery of the first surface of the first moldportion.

In some implementations, the first and second surfaces can be arrangedopposite each other prior to dispensing the photocurable material.

In some implementations, the first and second surfaces can be arrangedopposite each other after dispensing the photocurable material.

In some implementations, the first and second areas can be registeredwith respect to each other based on one or more fiducial markings on thefirst and/or second surfaces. The fiducial markings can be locatedoutside of the first and second areas.

In some implementations, the relative separation between the first andsecond surfaces can be controlled based on one or more spacers locatedon the first and/or second surfaces. The one or more spacers can belocated outside of the first and second areas.

In some implementations, the edge region of the first and/or second moldportions can include a material that repels the photocurable material.

In some implementations, the edge region of the first and/or second moldportions can include a patterned surface configured to pin droplets ofthe photocurable material.

In some implementations, the edge region of the first and/or second moldportions can include a patterned surface configured to roll droplets ofthe photocurable material.

In some implementations, the waveguide part can have a thickness of nomore than 1000 μm, an area of at least 1 cm².

In another aspect, a method includes assembling a head mounted displayincluding the waveguide part formed using one or more of the methodsdescribed herein.

In another aspect, a mold system for forming a waveguide part having apredetermined shape includes a first mold portion and a second moldportion. The first mold portion has a first surface including adiscrete, continuous first area corresponding to the predetermined shapeof the waveguide part. The first area is bounded by an edge region. Thesecond mold portion has a second surface including a discrete,continuous second area corresponding to the predetermined shape of thewaveguide part. The second area is bounded by an edge region having adifferent surface chemistry and/or surface structure than the secondarea. The system also includes one or more spacers on the first and/orsecond surfaces located outside of the first and second areas,respectively. The system also includes one or more fiducial markings onthe first and/or second surfaces located outside of the first and secondareas, respectively. The edge region of the first and second surfaceseach have a different surface chemistry and/or surface structure thanthe first area and second areas, respectively, such that a surfaceenergy of a photocurable material for forming the waveguide part isdifferent at the edge regions compared to the first and second areas,respectively.

Implementations of this aspect can include one or more of the followingfeatures.

In some implementations, the edge region of the first and/or second moldportions can include a patterned surface configured to pin droplets ofthe photocurable material.

In some implementations, the edge region of the first and/or second moldportions can include a patterned surface configured to roll droplets ofthe photocurable material.

In some implementations, the edge region of the first and/or second moldportions can include a patterned surface comprising structures having aheight in a range from 1 μm to 10 μm.

In some implementations, the edge region of the first and/or second moldportions can include a patterned surface comprising structures having alateral spacing in a range from 50 μm to 200 μm.

In some implementations, the edge region of the first and/or second moldportions can include a material that repels the photocurable material.

In some implementations, both the first surface and the second surfacecan include multiple discrete, continuous areas corresponding to thepredetermined shape of the waveguide part, each being bounded by acorresponding edge region.

In some implementations, the system can further include a dispensingstation configured to dispense a metered amount of photocurable materialinto a space adjacent the first area of the first mold portion.

In some implementations, the system can further include an irradiationstation configured to irradiate photocurable material in a space betweenfirst and second areas of the first and second surfaces.

In some implementations, the waveguide part can have a thickness of nomore than 1000 μm, an area of at least 1 cm².

In another aspect, a method of forming a waveguide film includesdispensing a photocurable material into a space between a first moldportion and a second mold portion opposite the first mold portion,adjusting a relative separation between a surface of the first moldportion with respect to a surface of the second mold portion opposingthe surface of the first mold portion, and irradiating the photocurablematerial in the space with radiation suitable for photocuring thephotocurable material to form a cured waveguide film. Further, themethod includes, concurrent to irradiating the photocurable material,performing at least one of varying the relative separation between thesurface of the first mold portion and the surface of the second moldportion, and varying an intensity of the radiation irradiating thephotocurable material.

Implementations of this aspect can include one or more of the followingfeatures.

In some implementations, the relative separation can be varied toregulate a force experienced by the first mold portion along an axisextending between the first mold portion and the second mold portion.The relative separation can be varied based on a closed-loop controlsystem that regulates the force.

In some implementations, the relative separation can be varied afterirradiating the photocurable material for a time sufficient to reach agel point in the photocurable material. The relative separation can bereduced after irradiating the photocurable material for the timesufficient to reach the gel point in the photocurable material

In some implementations, varying the relative separation can includemoving the first mold portion towards the second mold portion tocompress one or more spacer structures disposed between the first moldportion and the second mold portion. The spacer structures can becompressed according to an open-loop control system.

In some implementations, varying the relative separation can includeoscillating the position of the first mold portion relative to thesecond mold portion.

In some implementations, varying the intensity of the radiation caninclude varying a spatial intensity pattern irradiating the photocurablematerial.

In some implementations, varying the intensity of the radiation caninclude varying a power of the radiation. Varying the power can includepulsing the radiation. Each pulse of the radiation can have the samepower. Pulses of the radiation can have different power. Each pulse ofthe radiation can have the same duration. Pulses of the radiation canhave different durations. A pulse frequency can be constant. A pulsefrequency can be varied.

In some implementations, varying the intensity of the radiation caninclude sequentially irradiating different areas of the space.

In some implementations, the thickness of the space filled withphotocurable material can vary and the intensity of the radiation can bevaried so that regions of high relative thickness receive a higherradiation dose compared to regions of low relative thickness.

In some implementations, the method can further include separating thecured waveguide film from the first mold portion and the second moldportion.

In another example, a method can include assembling a head mounteddisplay comprising the waveguide film formed using one or more of themethods described herein.

The details of one or more embodiments are set forth in the accompanyingdrawings and the description below. Other features and advantages willbe apparent from the description and drawings, and from the claims.

DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram of an example system for producing polymer.

FIG. 2 is a diagram of example mold structures with spacing structures.

FIGS. 3A and 3B are diagrams of example mold structures and examplespacing structures.

FIGS. 4A and 4B are diagrams of example mold structures and examplespacing structures.

FIGS. 5A and 5B are diagrams of example mold structures, example spacingstructures, and example recesses.

FIG. 5C is a diagram of an example mold structure and example spacingstructures.

FIG. 5D is a diagram of an example mold structure and example recesses.

FIGS. 6A and 6B are diagrams of example mold structures, example spacingstructures, and example recesses.

FIGS. 7A and 7B are diagrams of example mold structures, example spacingstructures, and example recesses.

FIG. 8 is a diagram of example mold structures, example, spacingstructures, and example recesses.

FIG. 9 is a diagram of an example system for producing polymer.

FIG. 10 is a diagram of a cross-section of an example optical film.

FIG. 11 is a flow chart diagram of an example process for producing apolymer product.

FIG. 12 is a schematic diagram of an example process for producing asingle polymer product

FIGS. 13A-13E are diagrams of example patterns for dispensingphotocurable material.

FIG. 14 is a diagram of an example mold structure.

FIG. 15 is a diagram of another example mold structure.

FIG. 16A is a diagram of another example mold structure.

FIG. 16B is a diagram of an example etched grating pattern.

FIG. 17 is a diagram of another example mold structure.

FIG. 18 is a flow chart diagram of an example process for producing apolymer product.

FIG. 19A is a diagram of an example polymer film during the casting andcuring process.

FIG. 19B is a diagram of an example polymer film after curing andextraction.

FIG. 20 is a diagram of an example distribution of light for curing aphotocurable material.

FIGS. 21A and 21B are images of example polymer films.

FIG. 22A is a diagram of an example system for regulating stresseswithin a photocurable material during curing.

FIG. 22B is a diagram of another example system for regulating stresseswithin a photocurable material during curing.

FIG. 23 is a diagram of another example system for regulating stresseswithin a photocurable material during curing.

FIGS. 24A-24C are diagrams of example lighting patterns for curingphotocurable material.

FIG. 25 is a diagram of additional example lighting patterns for curingphotocurable material.

FIG. 26 is a diagram of additional example lighting patterns for curingphotocurable material.

FIG. 27A is a diagram of an additional example lighting pattern forcuring photocurable material.

FIG. 27B is a diagram of additional example lighting pattern for curingphotocurable material.

FIGS. 28A and 28B are diagram of example polymer products.

FIG. 29 is a flow chart diagram of an example process for producing apolymer product.

FIG. 30 is a diagram of an example computer system.

DETAILED DESCRIPTION

System and techniques for producing polymer film are described herein.One or more of the described implementations can be used to producepolymer film in a highly precise, controlled, and reproducible manner.The resulting polymer films can be used in a variety ofvariation-sensitive applications (e.g., as a part of eyepieces in anoptical imaging system).

In some implementations, polymer films can be produced such thatwrinkles, uneven thicknesses, or other unintended physical distortionsare eliminated or otherwise reduced. This can be useful, for example, asthe resulting polymer film exhibits more predictable physical and/oroptical properties. For example, polymer films produced in this mannercan diffract light in a more predictable and consistent manner, andthus, may be more suitable for use a high resolution optical imagingsystem. In some cases, optical imaging systems using these polymer filmscan produce sharper and/or higher resolution images than might otherwisebe possible with other polymer films.

An example system 100 for producing polymer film is shown in FIG. 1. Thesystem 100 includes two actuable stages 102 a and 102 b, two moldstructures 104 a and 104 b, two light sources 106 a and 106 b, a supportframe 108, and a control module 110.

During operation of the system 100, the two mold structures 104 a and104 b (also referred to as “optical flats”) are secured to the actuablestages 102 a and 102 b, respectively (e.g., through clamps 112 a and 112b). In some cases, the clamps 112 a and 112 b can be magnetic (e.g.,electromagnets) and/or pneumatic clamps that enable the mold structures104 a and 104 b to be reversibly mounted to and removed from theactuable stages 102 a and 102 b. In some cases, the clamps 112 a and 112b can be controlled by a switch and/or by the control module 110 (e.g.,by selectively applying electricity to the electromagnets of the clamps112 a and 112 b and/or selectively actuating pneumatic mechanisms toengage or disengage the molds structures).

A photocurable material 114 (e.g., a photopolymer or light-activatedresin that hardens when exposed to light) is deposited into the moldstructure 104 b. The mold structures 104 a and 104 b are moved intoproximity with one another (e.g., by moving the actuable stages 102 aand/or 102 b vertically along the support frame 108), such that thephotocurable material 114 is enclosed by the mold structures 104 a and104 b. The photocurable material 114 is then cured (e.g., by exposingthe photocurable material 114 to light from the light sources 106 aand/or 106 b), forming a thin film having one or more features definedby the mold structures 104 a and 104 b. After the photocurable material114 has been cured, the mold structures 104 a and 104 b are moved awayfrom each other (e.g., by moving the actuable stages 102 a and/or 102 bvertically along the support frame 108), and the film is extracted.

The actuable stages 102 a and 102 b are configured to support the moldstructures 104 a and 104 b, respectively. Further, the actuable stages102 a and 102 b are configured to manipulate the mold structures 104 aand 104 b, respectively, in one or more dimensions to control a gapvolume 116 between the mold structures 104 a and 104 b.

For instance, in some cases, the actuable stage 102 a can translate themold structure 104 a along one or more axes. As an example, the actuablestage 102 a can translate the mold structure 104 a along an x-axis, ay-axis, and/or a z-axis in a Cartesian coordinate system (i.e., acoordinate system having three orthogonally arranged axes). In somecases, the actuable stage 102 a can rotate or tilt the mold structure104 a about one or more axes. As an example, the actuable stage 102 acan rotate the mold structure 104 a along an x-axis (e.g., to “roll” themold structure 104 a), a y-axis (e.g., to “pitch” the mold structure 104a), and/or a z-axis (e.g., to “yaw” the mold structure 104 a) in aCartesian coordinate system. Translation and/or rotation with respect toone or more other axes are also possible, either in addition to orinstead of those described above. Similarly, the actuable stage 102 bcan also translate the mold structure 104 b along one or more axesand/or rotate the mold structure 104 b about one or more axes.

In some cases, the actuable stages 102 a can manipulate the moldstructure 104 a according to one or more degrees of freedom (e.g., one,two, three, four, or more degrees of freedom). For instance, theactuable stage 102 a can manipulate the mold structure 104 a accordingto six degrees of freedom (e.g., translation along an x-axis, y-axis,and z-axis, and rotation about the x-axis, y-axis, and z-axis).Manipulation according to one or more other degrees of freedom is alsopossible, either in addition to or instead of those described above.Similarly, the actuable stage 102 b can also manipulate the moldstructure 104 b according to one or more degrees of freedom

In some cases, the actuable stages 102 a and 102 b can include one ormore motor assemblies configured to manipulate the mold structures 104 aand 104 b and control the gap volume 116. For example, the actuablestages 102 a and 102 b can include a motor assembly 118 configured tomanipulate the actuable stages 102 a and 102 b, thereby repositioningand/or reorienting the actuable stages 102 a and 102 b.

In the example shown in FIG. 1, the actuable 102 a and 102 b can both bemoved relative to the support frame 108 to control the gap volume 116.In some cases, however, one of the actuable stages can be moved relativeto the support frame 108, while the other can remain static with respectto the support frame 108. For example, in some cases, the actuable stage102 a can be configured to translate in one or more dimensions relativeto the support frame 108 through the motor assembly 118, while theactuable stage 102 b can be held static with respect to the supportframe 108.

The mold structures 104 a and 104 b collectively define an enclosure forthe photocurable material 114. For example, the mold structures 104 aand 104 b, when aligned together, can define a hollow mold region (e.g.,the gap volume 116), within which the photocurable material 114 can bedeposited and cured into a film. The mold structures 104 a and 104 b canalso define one or more structures in the resulting film. For example,the mold structures 104 a and 104 b can include one or more protrudingstructures (e., gratings) from the surfaces 120 a and/or 120 b thatimpart a corresponding channel in the resulting film. As anotherexample, the mold structures 104 a and 104 b can include one or morechannels defined in the surfaces 120 a and/or 120 b that impart acorresponding protruding structure in the resulting film. In some cases,the mold structures 104 a and 104 b can impart a particular pattern onone or both sides of the resulting film. In some cases, the moldstructures 104 a and 104 b need not impart any pattern of protrusionsand/or channels on the resulting film at all. In some cases, the moldstructures 104 a and 104 b can define a particular shape and pattern,such that the resulting film is suitable for use as an eyepiece in anoptical imaging system (e.g., such that the film has one or more lightdiffractive microstructures or nanostructures that impart particularoptical characteristics to the film).

In some cases, the surfaces of the mold structures 104 a and 104 b thatface each other can each be substantially flat, such that the gap volume116 defined between them exhibits a TTV of 500 nm or less. For example,the mold structure 104 a can include a substantially flat surface 120 a,and the mold structure 104 b can have substantially flat surface 120 b.A substantially flat surface can be, for example, a surface thatdeviates from a flatness of an ideal flat surface (e.g., a perfectlyflat surface) by 100 nm or less (e.g., 100 nm or less, 75 nm or less, 50nm or less, etc.). A substantially flat surface can also have a localroughness of 2 nm or less (e.g., 2 nm or less, 1.5 nm or less, 1 nm orless, etc.) and/or an edge-to edge flatness of 500 nm or less (e.g., 500nm or less, 400 nm or less, 300 nm or less, 50 nm or less, etc.). Insome cases, one or both of the surfaces of the mold structures 104 a and104 b can be polished (e.g. to further increase the flatness of thesurfaces). A substantially flat surface can be beneficial, for example,as it enables the mold structures 104 a and 104 b to define a gap volume116 that is substantially consistent in thickness along the extent ofthe mold structures 104 a and 104 b (e.g., having a TTV of 500 nm orless). Thus, the resulting optical films can be flat (e.g., having atotal thickness variation [TTV] and/or a local thickness variation [LTV]less than or equal to a particular threshold value, for example lessthan 500 nm, less than 400 nm, less than 300 nm, etc.). Further,polished mold structures 104 a and 104 b can be beneficial, for example,in providing smoother optical films for optical imaging applications. Asan example, eyepieces constructed from smoother optical films mayexhibit improved imaging contrast.

The TTV and LTV of an example optical film 1000 are shown in FIG. 10.The TTV of the optical film 1000 refers to the maximum thickness of theoptical film 1000 with respect to the entirety of the optical film 1000(T_(max)), minus the minimum thickness of the optical film 1000 withrespect to the entirety of the optical film 1000 (T_(min)) (e.g.,TTV=T_(max)−T_(min)). The LTV of the optical film 1000 refers to themaximum thickness of the optical film 1000 with respect to a localizedportion of the optical film 1000 (T_(local max)), minus the minimumthickness of optical film 1000 with respect to the localized portion ofthe optical film 1000 (T_(local min)) (e.g.,LTV=T_(local max)−T_(local min)).

The size of the localized portion can differ, depending on theapplication. For example, in some cases, the localized portion can bedefined as a portion of the optical film having a particular surfacearea. For instance, for optical films intended for used as eyepieces inan optical imaging system, the surface area of the localized portion canbe an area having a 2.5-inch diameter. In some cases, the surface areaof the localized portion can differ, depending on the eyepiece design.In some cases, the surface area of the localized portion can differ,depending on the dimensions and/or features of the optical film.

The mold structures 104 a and 104 b are also rigid, such that they donot flex or bend during the film production process. The rigidity of themold structures 104 a and 104 b can be expressed in terms of its bendingstiffness, which is a function of the elastic modulus of the moldstructures (E) and the second moment of area of the mold structures (l).In some cases, the mold structures each can have a bending stiffness of1.5 Nm² or greater.

Further still, the mold structures 104 a and 104 b can be partially orfully transparent to radiation at one or more wavelengths suitable forphotocuring the photocurable material (e.g., between 315 nm and 430 nm).Further still, the mold structures 104 a and 104 b can the made from amaterial that is thermally stable (e.g., does not change in size orshape) up to a particular threshold temperature (e.g., up to at least200° C.). For example, the mold structures 104 a and 104 b can be madeof glass, silicon, quartz, Teflon, and/or poly-dimethyl-siloxane (PDMS),among other materials.

In some cases, the mold structures 104 a and 104 b can have a thicknessgreater than a particular threshold value (e.g., thicker than 1 mm,thicker than 2 mm, etc.). This can be beneficial, for example, as asufficiently thick mold structure is more difficult to bend. Thus, theresulting film is less likely to exhibit irregularities in thickness. Insome cases, the thickness of the mold structures 104 a and 104 b can bewithin a particular range. For example, each of the mold structures 104a and 104 b can be between 1 mm and 50 mm thick. The upper limit of therange could correspond, for example, to limitations of an etching toolused to pattern the mold structures 104 a and 104 b. In practice, otherranges are also possible, depending on the implementation.

Similarly, in some cases, the mold structures 104 a and 104 b can have adiameter greater than a particular threshold value (e.g., greater than 3inches). This can be beneficial, for example, as it enables relativelylarger films and/or multiple individual films to be producedsimultaneously. Further, if unintended particulate matter is entrappedbetween the mold structures (e.g., between a spacer structure 124 and anopposing mold structure 104 a or 104 b, such as at a position 126), itseffect on the flatness of the resulting filming film is lessened.

For instance, for mold structures 104 a and 104 b having a relativelysmall diameter, a misalignment on one side of the mold structures 104 aand 104 b (e.g., due to entrapped particulate matter on one of thespacer structures 124, such as at the position 126) may result in arelatively sharper change in thickness in the gap volume 116 along theextent to the mold structures 104 a and 104 b. Thus, the resulting filmor films exhibit more sudden changes in thickness (e.g., a steeper slopein thickness along the length of the film).

However, for mold structures 104 a and 104 b having a comparativelylarger diameter, a misalignment on one side of the mold structures 104 aand 104 b will result in a more gradual change in thickness in the gapvolume 116 along the extent to the mold structures 104 a and 104 b.Thus, the resulting film or films exhibit less sudden changes inthickness (e.g., a comparatively more gradual slope in thickness alongthe length of the film). Accordingly, mold structures 104 a and 104 bhaving a sufficiently large diameter are more “forgiving” with respectto entrapped particulate matter, and thus can be used to produce moreconsistent and/or flatter films.

As an example, if a particle of 5 μm or less is entrapped along a pointat the periphery of the mold structures 104 a and 104 b (e.g., at theposition 126), and the mold structures 104 a and 104 b each have adiameter of 8 inches, a gap volume having a horizontal surface area of 2square inches within the extent of the mold structures 104 a and 104 bwill still have a TTV of 500 nm or less. Thus, if a photocurablematerial is deposited within the gap volume, the resulting film willsimilarly exhibit a TTV of 500 nm or less.

The light sources 106 a and 106 b are configured to generate radiationat one or more wavelengths suitable for photocuring the photocurablematerial 114. The one or more wavelengths can differ, depending on thetype of photocurable material used. For example, in some cases, aphotocurable material (e.g., an ultraviolet light-curable liquidsilicone elastomer such as Poly(methyl methacrylate) orPoly(dimethylsiloxane)) can be used, and correspondingly the lightsource can be configured to generate radiation having a wavelength in arange from 315 nm to 430 nm to photocure the photocurable material. Insome cases, one or more of the mold structures 104 a and 104 b can betransparent, or substantially transparent to radiation at the suitablefor photocuring the photocurable material 114, such that radiation fromthe light sources 106 a and/or 106 b can pass through the moldstructures 104 a and/or 104 b and impinge upon the photocurable material114.

The control module 110 is communicatively coupled to the actuable stages102 a and 102 b, and is configured to control the gap volume 116. Forinstance, the control module 110 can receive measurements regarding gapvolume 116 (e.g., the distance between the mold structures 104 a and 104b at one or more locations) from the sensor assembly 122 (e.g., a devicehaving one or more capacitive and/or pressure-sensitive sensor elements)and reposition and/or reorient one or both of the mold structures 104 aand 104 b in response (e.g., by transmitting commands to the actuablestages 102 a and 102 b).

As described herein, to improve the quality and consistency of the film,the position of the two molds can be precisely controlled, such that themolds are kept parallel to each other immediately prior to and/or duringthe curing of the material. In some cases, this can be achieved, atleast in part, through the use of physical registration featurespositioned on one or more of the molds.

As an example as shown in FIG. 1, the system 100 can include one or morespacer structures 124 (e.g., protrusions or gaskets) that project fromone or more surfaces of the mold structure (e.g., mold structure 104 b)and towards an opposing mold structure (e.g., mold structure 104 a). Thespacer structures 124 can each have a substantially equal verticalheight, such that when the mold structures 104 a and 104 b are broughttogether (e.g., pressed together), the spacer structures 124 abut themold structures 104 a and 104 b and a substantially flat gap volume 116is defined between them.

Further, spacer structures 124 can be positioned in proximity to and atleast partially enclosing the area of the mold structures 104 a and 104b for receiving and curing the photocurable material 114. This can bebeneficial, for example, as it enables the system 100 to produce polymerfilms having a low TTV and/or LTV, without necessarily requiring that alow TTV and/or LTV be maintained across the entirety of the extend ofthe mold structures 104 a and 104 b. For example, multiple differentpolymer films can be produced without the need of achieving low TTV overthe entire volume between the mold structures 104 a and 104 b.Accordingly, the throughput of the production process can be increased.

For example, FIG. 2 shows an example mold structures 104 a and 104 bwith spacer structures 124 disposed between them. When the moldstructures 104 a and 104 b are brought together, the spacer structures124 abut the mold structures 104 a and 104 b and physically obstruct themold structures 104 a and 104 b from getting any nearer to each otherthan the vertical height 202 of the spacer structures 124. As thevertical height 202 of each of the spacer structures 124 issubstantially equal, a substantially flat gap volume 116 is definedbetween the mold structures 104 a and 104 b. In some cases, the verticalheight 202 of the spacer structures 124 can be substantially equal tothe desired thickness of the resulting film.

The spacer structures 124 can be constructed from various materials. Insome cases, the spacer structures 124 can be constructed from a materialthat is thermally stable (e.g., does not change in size or shape) up toa particular threshold temperature (e.g., up to at least 200° C.). Forexample, the spacer structures 124 can be made of glass, silicon,quartz, and/or Teflon, among other materials. In some cases, the spacerstructures 124 can be constructed from the same material as the moldstructures 104 a and/or 104 b. In some cases, the spacer structures 124can be constructed from a different material as the mold structures 104a and/or 104 b. In some cases, one or more of the spacer structures 124can be integrally formed with the mold structures 104 a and/or 104 b(e.g., etched from the mold structures 104 a and/or 104 b, imprintedonto the mold structures 104 a and/or 104 b through a lithographicmanufacturing processes, or additively formed onto the mold structures104 a and/or 104 b such as through an additive manufacturing processes).In some cases, one or more of the spacer structures 124 can be discretefrom the mold structures 104 a and/or 104 b, and can be secured oraffixed to the mold structures 104 a and/or 104 b (e.g., using glue orother adhesive).

Although two spacer structures 124 are shown in FIG. 2, this is merelyan illustrative example. In practice, there can be any number of spacerstructures 124 (e.g., one, two, three, four, or more) protruding fromthe mold structure 104 a, the mold structure 104 b, or both. Furtherstill, although FIG. 2 shows the spacer structures 124 positioned alonga periphery of the mold structures 104 a and 104 b, in practice, eachspacer structures 124 can be positioned anywhere along the extent of themold structures 104 a and 104 b.

For instance, FIG. 3A shows an example mold structure 104 b havingmultiple spacer structures 124 positioned along a periphery of thesurface 120 b. Further, the spacer structures 124 surround an area 302of the surface 120 b for receiving the photocurable material 114.Accordingly, when a portion of photocurable material 114 is depositedalong the area 302 and the mold structure 104 b is brought together withanother mold structure 104 a, the spacer structures 124 abut the moldstructures 104 a and 104 b and physically obstruct the mold structures104 a and 104 b from getting any nearer to each other than the verticalheight of the spacer structures 124. Thus, when the photocurablematerial 114 is cured, the resulting film will have a constant heightdefined by the vertical height of the spacer structures 124.

FIG. 3B shows another example mold structure 104 b having multiplespacer structures 124. In this example, the spacer structures 124 arepositioned along a periphery of the surface 120 b, as well as dispersedalong an interior of the surface 120 b. Further, the spacer structures124 surround multiple different areas 304 of the surface 120 b forreceiving the photocurable material 114. Accordingly, when portions ofphotocurable material 114 is deposited along each of the areas 304 andthe mold structure 104 b is brought together with another mold structure104 a, the spacer structures 124 abut the mold structures 104 a and 104b and physically obstruct the mold structures 104 a and 104 b fromgetting any nearer to each other than the vertical height of the spacerstructures 124. Thus, when the photocurable material 114 is cured, theresulting films will each have a constant height defined by the verticalheight of the spacer structures 124.

In some cases, spacer structures can define a continuous perimeteraround an area of the mold structure for receiving photocurable material(e.g., a continuous gasket that surrounds the area). In some cases,spacer structures can define a discontinuous perimeter around an area ofthe mold structure for receiving photocurable material (e.g., analternating sequence of protrusions and gaps that that surround thearea). In some cases, spacer structures can define one or morecontinuous perimeters and/or one or more discontinuous perimeters aroundan area.

As an example, FIG. 4A shows an overhead view of an example moldstructure 104 b. The mold structure 104 b has multiple sets of spacerstructures 124 a-d. In this example, a first set of spacer structures124 a are positioned along a periphery of the surface 120 b. Further, asecond set of spacer structures defines a continuous perimeter (e.g., arectangular perimeter) around a first area 402 a for receivingphotocurable material 114. Further, a third set of spacer structures 124c defines a discontinuous perimeter (e.g., a circular perimeter) arounda second area 402 b for receiving photocurable material 114. Further, afourth set of spacer structures 124 d defines another discontinuousperimeter (e.g., a polygonal perimeter) around a third area 402 c forreceiving photocurable material 114. In this matter, multiple differentspacer structures can be positioned along different areas for receivingphotocurable materials, such that the resulting films from each of thoseareas will each have a constant height. Although example perimetershapes are shown in FIG. 4A, these are merely illustrative examples. Inpractice, sets of spacer structures can define perimeters having anyshape, such as circular shapes, elliptical shapes, rectangular shapes,polygonal shapes, or any other shape.

In some cases, spacer structures can define a perimeter along an edgethe mold structure. As an example, FIG. 4B shows an overhead view ofanother example mold structure 104 b. The mold structure 104 b shown inFIG. 4B is similar in some respects to that shown in FIG. 4A. Forexample, in FIG. 4B, the mold structure 104 b has a first set of spacerstructures 124 a positioned along a periphery of the surface 120 b, asecond set of spacer structures defining a continuous perimeter (e.g., arectangular perimeter) around a first area 402 a for receivingphotocurable material 114, a third set of spacer structures 124 cdefining a discontinuous perimeter (e.g., a circular perimeter) around asecond area 402 b for receiving photocurable material 114, and a fourthset of spacer structures 124 d defining another discontinuous perimeter(e.g., a polygonal perimeter) around a third area 402 c for receivingphotocurable material 114. In this example, however, the mold structure104 b further includes a fifth set of spacer structures 124 e defining adiscontinuous perimeter (e.g., a circular perimeter defined by fourarc-like portions) along an edge 400 of the mold structure 104 b. Theperimeter defined by the spacer structures 124 e encloses each of theother spacer structures of the mold structure 104 b (e.g., the spacerstructures 124 a-d). This set of enclosing spacer structures 124 e canbe useful, for example, in further controlling the position of the twomolds relative to one another. Thus, the quality and consistency of theresulting film can be further improved.

As shown in FIG. 4B, a set of enclosing spacer structures (e.g., the setof spacer structures 124 e) can define a discontinuous perimeter.However, this need not be the case. For example, in some cases, a set ofenclosing spacer structures can define a continuous perimeter around theother spacer structures of a mold structure. Further as shown in FIG.4B, a set of enclosing spacer structures can define a circularperimeter. However, this also need not be the case. For example, in somecases, a set of enclosing spacer structure can define other shapes(e.g., a circular shape an elliptical shape, a rectangular shape, apolygonal shape, or any other shape). Further still, in some cases, theshape of the perimeter defined by the set of enclosing spacer structurescan be similar to or identical to the shape defined by the edge 400. Forexample, as shown in FIG. 4B, both can be circular in shape. In somecases, the shape of the perimeter defined by the set of enclosing spacerstructures can be different than the shape defined by the edge 400. Forexample, one can be circular in shape, and the other can be polygonal inshape.

As described herein, in some cases, mold structures can include one ormore recesses (e.g., grooves) defined along one or more surfaces of themold structure that accept one or more spacer structures from anopposing mold structure. The spacer structures and/or recesses can beused to physically align the molds, such that the relative orientationof the mold surfaces are less likely to deviate from the intendedorientation. For example, the spacer structures and/or recesses can beused to maintain a parallel orientation between two molds. As a result,the photocurable material has a more even thickness, and is less likelyto become distorted.

As an example, FIG. 5A shows example mold structures 104 a and 104 b.The mold structure 104 b includes spacer structures 502 a and 502 bpositioned along a periphery of the surface 120 b. In this example thespacer structure 502 a has a corresponding recess 504 a defined on thesurface 120 a of the opposing mold structure 104 a, while the spacerstructures 504 b does not. When portions of photocurable material 114are deposited along an area 506 and the mold structures 104 a and 104 bare brought together, the spacer structures 502 a and 504 a abut themold structures 104 a and 104 b and physically obstruct the moldstructures 104 a and 104 b from getting any nearer to each other thaneither the vertical height of the spacer structure 502 b, or thevertical height of the spacer structure 502 a minus a vertical depth ofthe recess structure 504 a.

For example, the spacer structure 502 a slots or inserts into the recess504 a, which prevents the mold structures 104 a and 104 b from gettingany nearer of each other. Further, due to the walls of the recess 504 a,the spacer structure 502 a is horizontally secured within the recess 504a. Accordingly, the mold structure 104 a and 104 b cannot horizontallymove with respect to another. As another example, the spacer structure502 b does not have a corresponding recess, and instead directly abutsthe surface 120 a of the mold structure 104 a. Thus, although the spacerstructure 502 b also prevents the mold structures 104 a and 104 b fromgetting any nearer to each other, the spacer structure 502 b does nothorizontally secure the mold structures 104 a and 104 b relative to oneanother.

Further, as shown in FIG. 5A, the mold structures 104 a and 104 b alsodefine a pattern of gratings 508 along the area 506. Thus, when thephotocurable material 114 is cured, the resulting film will have aparticular pattern of gratings defined along its length.

Although example spacer structure and recess shapes as shown in FIG. 5A,these are merely illustrative examples. In practice, the shape of eachspacer structure and/or recess can vary, depending on theimplementation. As an example, FIG. 5B shows another example moldstructure 104 a and another example mold structure 104 b. In thisexample, the mold structure 104 b includes spacer structures 502 c and502 d positioned along a periphery of the surface 120 b, each having acorresponding recess 504 b and 504 c, respectively, defined on thesurface 120 a of the opposing mold structure 104 a.

The spacer structure 502 c and the recess 504 b have correspondingtriangular cross-sections. Accordingly, when the mold structures 104 aand 104 b are brought together, the spacer structure 502 c slots orinserts into the recess 504 b, which prevents the mold structures 104 aand 104 b from getting any nearer of each other than a distance d.Further, due to the walls of the recess 504 b, the spacer structure 502b is horizontally secured within the recess 504 b. Accordingly, the moldstructure 104 a and 104 b cannot horizontally move with respect toanother example.

However, the spacer structures and recesses need not have identicalcross-sectional shapes. For example, as shown in FIG. 5B, the spacerstructure 502 d has a triangular cross-section, and the recess 504 c hasrectangular cross-section. Although the spacer structure 502 d and therecess 504 c are different cross-sectional shapes, the recess 504 c isconfigured to receive at least a portion of the spacer structure 502 d.Accordingly, when the mold structures 104 a and 104 b are broughttogether, the spacer structure 502 d slots or inserts partially into therecess 504 c, which prevents the mold structures 104 a and 104 b fromgetting any nearer of each other than a distance d. Further, due to thewalls of the recess 504 c, the spacer structure 502 d is similarlyhorizontally secured within the recess 504 c. Accordingly, the moldstructure 104 a and 104 b cannot horizontally move with respect toanother example.

Similarly, as shown in FIG. 5B, the mold structures 104 a and 104 b alsodefine a pattern of gratings 510 along an area 512. Thus, when thephotocurable material 114 is deposited into the area 512 and cured, theresulting film will have a particular pattern of gratings defined alongits length.

The dimensions of each of these features can vary, depending on theimplementation. In some implementations, the width of a spacer structurecan be between 0.01 cm to 1 cm. In some implementations, the height of aspacer structure can be between 100 μm and 900 μm. The geometry of thespacer structures can be rectangular prism, cylinder, and otherthree-dimensional shapes (e.g., a complex three-dimensional shape).

Further, each spacer structure and/or recess can be substantially flat.For instance, each spacer structure and/or recess can have a totalthickness variation of 100 nm or less, such that when a spacer structureand recess are brought together, the distance between their respectivemold structures deviate from an expected or designed distance by 100 nmor less. As an example, for a spacer structure and a recess each havinga respective rectangular cross section, the surfaces of the spacerstructure and the recesses can be sufficiently flat and accuratelyformed, such that when they are brought together, the distance betweentheir corresponding mold structures deviate from an expected or designeddistance by 100 nm or less. As another example, for a spacer structurehaving a triangular cross section and a recess having a rectangularcross section (e.g., as shown in FIG. 5B), the slopes of the triangularspacer structure and the surfaces of the recess can be sufficiently flatand accurately formed, such that when the spacer structure and recessare brought together, the distance between their corresponding moldstructures deviate from an expected or designed distance by 100 nm orless.

Further, although different spacer structures and recesses are shown inFIGS. 5A and 5B, there are merely illustrative examples. In practice,spacer structures and/or recess having different physical configurationsalso can be used, either instead or in addition to those shown. As anexample, as shown in FIG. 5C, a spacer structure 502 e can have aportion 514 with a rectangular cross-section, and a distal end 516having a substantially hemispherical shape. As another example, as shownin FIG. 5C, a spacer structure 502 f can have a portion 518 with arectangular cross-section, and a number of rounded corners 520 at itsdistal end 522. As another example, as shown in FIG. 5C, a spacerstructure 502 g can have a portion 524 with a trapezoidal cross-section(e.g., a triangle shape with a corner removed), and a rounded distal end526. As another example, a spacer structure can have a substantiallypolygonal cross-section (e.g., triangular, quadrilateral, pentagonal,hexagonal, etc.) with one or more rounded corners instead of sharpcorners.

Similarly, recesses can also include one or more rounded features. As anexample, as shown in FIG. 5D, a recess 504 e can have a portion 528 witha rectangular cross-section, and an interior end 530 having asubstantially hemispherical shape. As another example, as shown in FIG.5D, a recess 504 f can have a portion 532 with a rectangularcross-section, and a number of rounded corners 534 at its interior end536. As another example, as shown in FIG. 5D, a recess 504 g can have aportion 538 with a trapezoidal cross-section (e.g., a triangle shapewith a corner removed), and a rounded interior end 540. As anotherexample, a recess can have a substantially polygonal cross-section(e.g., triangular, quadrilateral, pentagonal, hexagonal, etc.) with oneor more rounded corners instead of sharp corners.

These configurations can be useful, for example, as they reduce oreliminate the presence of sharp edges or corners in the regions in whichthe spacer structures interface with their corresponding recesses. Thus,this can reduce wear and tear on the spacer structures and/or therecesses. Further, this can enable the mold structures to bettermaintain their flatness over repeated usages (e.g., by reducing pointcontacts between them).

In some cases, the system 100 (via the arrangement of the spacerstructures and corresponding recesses on the mold structures) canposition the mold structures such that the thickness of the gap volume116 (e.g., the distance between the mold structures) is between 20 μmand 2 mm. In some cases, the photocurable material 114 can be depositedinto at least one of the mold structures 104 a and 104 b prior to thesystem 100 positioning the mold structures 104 a and 104 b against eachother at this distance. This can be beneficial, for example, as it maybe easier or more convenient to introduce photocurable material 114while the mold structures are further apart, rather than when they arepositioned close together. Nevertheless, in some cases, photocurablematerial 114 can be deposited into the mold structures after they havebeen brought together (e.g., through an injection tube or needlepositioned through one or more of the mold structures).

In the examples shown in FIGS. 5A and 5B, some of the spacer structures(e.g., spacer structures 502 a, 502 c, and 502 d) are configured to slotor insert, at least partially, into a corresponding recess (e.g.,recesses 504 a, 504 b, and 504 c, respectively), such that the spacerstructures are horizontally secured within the recesses. In thisconfiguration, the spacer structure is “locked” within a correspondingrecess, and cannot move relative to the recess along any horizontaldirection.

However, in some cases, spacer structures and recesses can be configuredsuch that in a slotted configuration, the spacer structure retains oneor more horizontal degrees of freedom relative to the recess. Forexample, in some cases, a spacer structure and a recess can beconfigured such that when the spacer structure is slotted into therecess, the recess prevents the spacer structure from moving withrespect to the recess along one or more first horizontal directions, butallows the spacer structure to move with respect to the recess along oneor more second horizontal directions.

As an example, FIG. 6A shows an overhead view of another example moldstructure 104 a (indicated in outline) overlaid atop another examplemold structure 104 b (indicated using shaded shapes). The mold structure104 b includes spacer structures 602 a-c positioned around an area 606between the mold structures 104 a and 104 b. Further, each of the spacerstructures 602 a-c has a corresponding recess 604 a-c defined along thesurface of the mold structure 104 a. When portions of photocurablematerial 114 is deposited along the area 606 and the mold structures 104a and 104 b are brought together, the spacer structures 602 a-c slotinto the recesses 604 a-c and physically obstruct the mold structures104 a and 104 b from getting any nearer to each other.

Further, each recess 604 a-c has a cross-section area that is largerthan its corresponding spacer structure 602 a-c, and defines a slot orpath along which the spacer structure 602 a-c can horizontally translatewithin it. For example, the recess 604 a defines a slot or path thatenables the spacer structure 602 a to slide within it along a direction608 a. A cross-sectional view of the interaction between the recess 604a and the spacer structure 602 a is shown in FIG. 6B. Further, therecess 604 b defines a slot or path that enables the spacer structure602 b to slide within it along a direction 608 b. Further still, therecess 604 c defines a slot or path that enables the spacer structure602 c to slide within it along a direction 608 c. However, as thedirections 608 a-c are not parallel to each other, when all of thespacer structures 602 a-c are slotted within their correspondingrecesses 604 a-c, the mold structures 102 a and 102 b are horizontallylocked to one another. Thus, multiple different sets of spacerstructures and recesses can be used to register the position of one moldstructure relative to another in a “self-locking” manner.

Nevertheless, in some cases, a spacer structure and a recess can beconfigured such that when the spacer structure is slotted into therecess, the spacer structure is locked within a corresponding recess,and cannot move relative to the recess along any horizontal direction.

As an example, FIG. 7A shows an overhead view of another example moldstructure 104 a (indicated in outline) overlaid atop another examplemold structure 104 b (indicated using shaded shapes). The mold structure104 b includes spacer structures 702 a and 702 b positioned around anarea 706 between the mold structures 104 a and 104 b. Further, each ofthe spacer structures 702 a and 702 b has a corresponding recess 704 aand 704 b defined along the surface of the mold structure 104 a. Whenportions of photocurable material 114 is deposited along the area 706and the mold structures 104 a and 104 b are brought together, the spacerstructures 702 a and 702 b slot into the recesses 704 a and 704 b andphysically obstruct the mold structures 104 a and 104 b from getting anynearer to each other. Further, each recess 704 a and 704 b has across-sectional area and a shape similar to those of its correspondingspacer structure 702 a and 704 b. A cross-sectional view of theinteraction between the recess 704 a and the spacer structure 702 a isshown in FIG. 7B. Thus, when each spacer structure 702 a and 702 b isslotted into its corresponding recess 704 a and 704 b, it is snugglyretained within the recess and cannot move relative to the recess alongany horizontal direction.

As described herein, although various example spacer structures andrecesses are shown and described, it is understood that any combinationof spacer structures and recesses can be used in any particularembodiment. As an example, FIG. 8 shows an overhead view of anotherexample mold structure 104 a (indicated in outline) overlaid atopanother example mold structure 104 b (indicated using shaded shapes).The mold structure 104 a includes several different spacer structures802 a-h positioned around an area 806 between the mold structures 104 aand 104 b. Further, each of the spacer structures 802 a-h has adifferent corresponding recess 804 a-h defined along the surface of themold structure 104 b. As shown in FIG. 8, some of the sets of spacerstructures and recesses allow for relative horizontal movement withrespect to one or more directions (e.g., spacer structure 802 d andrecess 804 d, and spacer structure 802 f and recess 804 f). Further,some of the sets of spacer structures and recesses do not allow forrelative horizontal movement (e.g., the remaining sets of spacerstructures and recesses shown in FIG. 8). In practice, othercombinations are also possible, depending on the implementation.

Further, although of the examples shown herein include spacer structuresprotruding from a common mold structure, this need not be the case. Inpractice, there can be any number of spacer structures (e.g., one, two,three, four, or more) protruding either from a single mold structure orfrom both mold structures. Further, although of the examples shownherein include recesses defined along a common mold structure, this alsoneed not be the case. In practice, there can be any number of recesses(e.g., one, two, three, four, or more) defined either along a singlemold structure or along both mold structures.

In some cases, spacer structures and/or recesses can be formed throughlithographical techniques. For example, spacer structures and/orrecesses can be patterned through lithography, and etched using dry etchtechniques such as reactive ion etch (ME), inductively coupled plasma(ICP) and/or sputter etch techniques. In some cases, spacer structuresand/or recesses can be etched in glass, silicon, and/or metalsubstrates.

Further, in some cases, spacer structures and/or recesses (e.g., thosehaving angled surfaces) can be implemented in glass, fused silica,silicon, metals, or other materials using gray-scale lithography. Forexample, gray-scale lithography can be used to pattern a three-dimensionresist layer as a mask, and transfer the geometries into a substrate bydry etch techniques such as RIE, ICP, and/or sputter etch. For siliconsubstrates, the angled sidewall surfaces can also be fabricated usingwet chemical etching (e.g., to define linear top-view shapes, such as onthe on x-y plane, depending on the crystalline orientation of thesilicon wafer used). For example, in (100) silicon wafer, the top-viewshapes/geometries of the spacer structures and/or recesses will align tothe <110> direction, and the sidewall will have 54.7° angle from thehorizon. The top-view shapes/geometries can be patterned throughlithography, and etched in the z direction using dry etch techniques(e.g., for hard mask) and then using wet etch techniques (e.g., forsilicon, such as KOH and TMAH).

In some cases, spacer structures can be formed through additivemanufacturing techniques (e.g., 3D printing and two-photon laserprinting). In some cases, the printed polymer structures can be directlyused as spacer structures. In some case, she printer polymer structurescan be used as three-dimension mask layer, and transfer the geometriesinto a substrate by dry etch techniques such as ME, ICP, and/or sputteretch.

In some cases, a system 100 can also include one or more heatingelements to apply heat to a photocurable material during the curingprocess. This can be beneficial, for example, in facilitating the curingprocess. For instance, in some cases, both heat and light can be used tocure the photocurable material. For example, the application of heat canbe used to accelerate the curing process, make the curing process moreefficient, and/or make the curing processes more consistent. In somecases, the curing process can be performed using heat instead of light.For example, the application of heat can be used to cure thephotocurable material, and a light source need not be used.

An example system 900 for producing polymer film is shown in FIG. 9. Ingeneral, the system 900 can be similar to the system 100 shown inFIG. 1. For example, the system 900 can include two actuable stages 102a and 102 b, two mold structures 104 a and 104 b, a support frame 108,and a control module 110. For ease of illustration, the control module110 is not shown in FIG. 9.

However, in this example, the system 900 does not include the two lightsources 106 a and 106 b. Instead, it includes two heating elements 902 aand 902 b, positioned adjacent to the mold structures 104 a and 104 b,respectively. The heating elements 902 a and 902 b are configured tomove with the mold structures 104 a and 104 b (e.g., through theactuable stages 102 a and 102 b), and are configured to apply heat tothe photocurable material 114 between the mold structures 104 a and 104b during the curing process.

The operation of the heating elements 902 a and 902 b can be controlledby the control module 110. For example, the control module 110 can becommunicatively coupled to the heating elements 902 and 902 b, and canselectively apply heat to the photocurable material 114 (e.g., bytransmitting commands to the heating elements 902 a and 902 b).

Example heating elements 902 a and 902 b metal heating elements (e.g.,nichrome or resistance wire), ceramic heating elements (e.g., molybdenumdisilicide or PTC ceramic elements), polymer PTC heating elements,composite heating elements, or a combination thereof. In some cases, theheating elements 902 a and 902 b can include a metal plate to facilitatea uniform transfer heat to the mold structures 104 a and 104 b.

Although two heating elements 902 a and 902 b are shown in FIG. 9, insome cases, a system can include any number of heating elements (e.g.,one, two, three, four, or more), or none at all. Further, although thesystem 900 is shown without light sources 106 a and 106 b, in somecases, a system can include one or more light sources and one or moreheating elements in conjunction.

FIG. 11 shows an example process 1100 for producing a polymer product.The process 1100 can be performed, for example, using the systems 100 or900. In some cases, the process 1100 can be used to produce polymerfilms suitable for use in optical applications (e.g., as a part ofeyepieces in an optical imaging system).

In the process 1100, mold structures are mounted to actuable stages(step 1102). For example, as shown in FIGS. 1 and 9, molds structures104 a and 104 b can be mounted to actuable stages 102 a and 102 b,respectively. The mold structures can be mounted using clamps (e.g.,clamps 112 a and 112 b) or other attachment mechanisms. In some cases,the mold structures can be mounted using electromagnetic or pneumaticclamps that are selectively controlled by a switch and/or a controlmodule.

One or more spacer structures are introduced between the mold structures(step 1104). As described herein, spacer structures can be disposed atvarious positions between the mold structures (e.g., as shown anddescribed with respect to FIGS. 1-9). In some cases, a spacer structurecan be integrally formed with a mold structure (e.g., etched from themold structures, imprinted onto the mold structures through alithographic manufacturing processes, or additively formed onto the moldstructures such as through addition manufacturing processes). In somecases, a spacer structure can be separate and distinct from the moldstructure, and can be individually positioned between the moldsstructures.

A photocurable material is dispensed between the mold structures (step1106). Example photocurable materials are described herein (e.g., withrespect to FIG. 1). In some cases, photocurable materials can bedispensed along one or more specific positions in a gap volume betweenthe mold positions, such that they are at least partially enclosed bythe spacer structures (e.g., as shown and described with respect toFIGS. 3A and 3B).

In some cases, the photocurable material can be dispensed differently,depending on the material. For example, for photocurable materials thatshrink a relatively small amount (e.g., less than 10%) during thepolymerization process and exhibit mechanical properties that are notdependent on the casting surface area, the photocurable material can becarried out all at once to cover a large area on the mold structure,while avoiding contact between the photocurable material and the spacerstructures (e.g., as shown in FIG. 3A).

As another example, for photocurable materials that shrink a relativelylarger amount (e.g., greater than 10%) and exhibit mechanical propertiesthat are dependent on the casting surface area, photocurable materialscan be dispensed on the bottom mold in metered quantities at multipledifferent locations, such that individual dispensed “puddles” of thematerial do not touch each other or the spacer structures (e.g., asshown in FIG. 3B). This can be beneficial, for example, as it reducesthe surface area of each individual the casted polymer material, suchthat each is small enough to shrink freely and cure more efficiently.This can result in a lower TTV and/or LTV, and can enable highermanufacturing throughput.

In some cases, the photocurable materials can be “pre-polymerized” priorto dispensing between the mold structures (e.g., such that they areshrunk, but still are sufficiently fluid to be effectively dispensedbetween the mold structures). A pre-polymerization process can beperformed, for example, by curing the photocurable materials (e.g.,using UV light and/or heat) at an energy level that makes the materialsviscous yet still able to flow.

The mold structures are positioned in proximity to each other (step1108). For example, as described with respect to FIGS. 1 and 9, theactuable stages 102 a and/or 102 b can move the mold structures 104 aand/or 104 b towards each other, such that the photocurable material 114is enclosed between them without a gap volume. In some cases, the moldstructures 104 a and 104 b can be positioned such that a mold structurecontacts a spacer structure positioned on the opposing mold structurewith a particular amount of positive force (e.g., 10 N to 200 N), andlocked into place.

The photocurable material is cured (step 1110). In some cases, thephotocurable material can be cured using light (e.g., as shown anddescribed with respect to FIG. 1). For example, the top and/or thebottom of the photocurable material can be irradiated with light (e.g.,ultraviolet light). In some cases, irradiating both sides of thephotocurable material can enable more uniform and faster curing. In somecases, the light intensity can be kept uniform across the area of thephotocurable material to reduce non-uniform shrinkage and itspotentially adverse consequences on the TTV and/or the LTV of resultingpolymer products. In some cases, a diffuser can be positioned between alight source and the photocurable material to improve the uniformity oflight.

In some cases, the photocurable material can be cured using heat (e.g.,as shown and described with respect to FIG. 9). In some cases, heat canbe applied along the top and/or the bottom of the photocurable material.In some cases, heating both sides of the photocurable material canenable more uniform and faster curing. In some cases, metal plates canbe positioned between a heating element and a molds structure tofacilitate a uniform distribution of heat across the mold structure andthe photocurable material.

Further, in some cases, the photocurable material can be cured usingboth light and heat. As an example, thermal curing can be initiated byexposure to infrared light. For instance, a photocurable material can bechosen on the basis that it absorbs relatively little infraredradiation. Further, the thermal heating of the photocurable material canbe localized in the photocurable material itself. This arrangement canbe beneficial, for example, in enabling lower molding cycle times asthere is less heat to be removed from the mold structure after eachcuring processes is performed. Further, if the photocurable materialrequires both thermal and light energy to cure quickly with optimumproperties, both sources could be applied from either side or both sidesof the mold structures.

After the photocurable material is cured, the resulting product isremoved from between the mold structures (step 1112). For example, themold structures can be positioned further from each other (e.g., usingthe actuable stages), and the product can be extracted from betweenthem. In some cases, the extracted product can have a particular shapesuitable for use in a particular application (e.g., as defined by themold structures) without requiring a separate singulation process (e.g.,separately cutting out a portion of the cured polymer product accordingto the desired shape). As described herein, in some cases, the productcan be a polymer film suitable for use in optical applications (e.g., asa part of eyepieces in an optical imaging system). In some cases, asmall opening in spacer structures can be used to evacuate excessphotocurable material from between the mold structures.

As described herein, in some cases, individual polymer products can beproduced without performing a singulation process. For example, twomolds can be configured such that, when the molds are brought together,they define an enclosed region corresponding to the size and shape ofsingle polymer product. During the production process, a photocurablematerial is enclosed between the two molds, and the material is cured toform a polymer film. After curing, the polymer film is extracted fromthe molds, resulting in a single polymer product having a particularpredefined size and shape. This polymer product can be subsequently usedin other manufacturing processes without the need for an additionalsingulation step. Accordingly, the polymer product is less likely tohave physical and/or chemical damage (e.g., compared to a polymerproduct formed through singulation of a larger polymer film), and can bemore suitable for use in variation-sensitive environments

FIG. 12 is a simplified schematic diagram of an example process forproducing a single polymer product 1200 using the system 100, withoutperforming a separate singulation process. The process shown in FIG. 12can be used, for example, to produce optical components, such aswaveguides or eyepieces for using a wearable imaging headsets. For easeof illustration, portions of the system 100 have been omitted.

In some cases, the process can be particularly useful for producingwaveguides or eyepieces suitable for use in a headset. For instance, theprocess can be used to produce waveguides or eyepieces having athickness and/or cross-sectional area that are sufficient to guide lightand project light covering a field of view of a headset wearer. As anexample, the process can be used to produce polymer products having athickness of no more than 1000 μm (e.g., as measured along the z-axis ofa Cartesian coordinate system), such as 800 μm or less, 600 μm or less,400 μm or less, 200 μm or less, 100 μm or less, or 50 μm or less, and anarea of at least 1 cm² (e.g., as measured with respect an x-y plane ofthe Cartesian coordinate system), such as 5 cm² or more, 10 cm² or more,such as up to about 100 cm² or less, and having a predetermined shape.In certain cases, the polymer film can have a dimension of at least 1 cm(e.g., 2 cm or more, 5 cm or more, 8 cm or more, 10 cm or more, such asabout 30 cm or less) in at least one direction in the x-y plane.

As shown in the left portion of FIG. 12, mold structure 104 a has asurface 120 a, and the mold structure 104 b has a surface 120 b facingthe surface 120 a of the mold structure 104 a. The mold structures 104 aand 104 b are configured such that, when the molds are brought together,they define an enclosed region corresponding to the size and shape ofsingle polymer product (e.g., a single waveguide or eyepiece). Forexample, the surface 120 a can include a discrete, continuous first area1202 a corresponding to the predetermined size and shape of the polymerproduct 1200. Similarly, the surface 120 b can include a discrete,continuous second area 1202 b corresponding to the predetermined sizeand shape of the polymer product 1200. When the mold structures 104 aand 104 b are aligned together, they can define a hollow mold region(e.g., a gap volume 116) along the areas 1202 a and 1202 b correspondingto the size and shape of the polymer product 1200, within which thephotocurable material 114 can be deposited and cured into a film. Insome cases, the areas 1202 and 1202 b can encompass substantially theentirety of the surfaces 120 a and 120 b, respectively. In some cases,the areas 1202 and 1202 b can encompass a portion of the surfaces 120 aand 120 b, respectively.

As described above, the mold structures 104 a and 104 b can also defineone or more structures in the resulting film. For example, the moldstructures 104 a and 104 b can include one or more protruding structuresfrom the surfaces 120 a and/or 120 b of the mold structures that imparta corresponding channel in the resulting film. As another example, themold structures 104 a and 104 b can include one or more channels definedin the surfaces 120 a and/or 120 b that impart a correspondingprotruding structure in the resulting film. In some cases, the moldstructures 104 a and 104 b can define a particular shape and pattern,such that the resulting film is suitable for use as a waveguide oreyepiece in an optical imaging system (e.g., such that the film has oneor more light diffractive microstructures or nanostructures that impartparticular optical characteristics to the film).

As shown in the left portion of FIG. 12, photocurable material 114 isdispensed onto the mold structures 104 a and/or 104 b (e.g., dispensedinto a space on or adjacent of the first area 1202 a and/or the secondarea 1202 b). In some cases, the photocurable material 114 can bedispensed by a dispensing station or mechanism, such as by one or morepumps, pipettes, injectors, syringes, etc. that selectively dispense ameter amount of photocurable material). The photocurable material 114can be dispensed according to different patterns. As an example, thephotocurable material 114 can be dispensed at multiple differentdiscrete locations along the first area 1202 a and/or the second area1202 b. As another example, the photocurable material 114 can bedispensed a single discrete location along the first area 1202 a and/orthe second area 1202 b. In some cases, the photocurable material 114 candispensed according to a symmetric pattern. In some cases, thephotocurable material 114 can be dispensed according to an asymmetricpattern. Further, at each discrete location, the dispensed photocurablematerial 114 can have a particular size, volume, and shape. Examplepatterns are shown and described in greater detail with respect to FIGS.13A-13E. In some cases, photocurable material 114 can be dispensed alonga single mold structure (e.g., the bottom mold structure 104 b). In somecases, photocurable material 114 can be dispensed along both moldstructures.

As shown in the upper middle portion of FIG. 12, the mold structures 104a and 104 b are moved into proximity with one another (e.g., by movingthe actuable stages 102 a and/or 102 b described with respect to FIG.1), such that the photocurable material 114 is enclosed by the moldstructures 104 a and 104 b. The photocurable material 114 can be held inplace by surface tension of the photocurable material 114 and/oradhesive forces between the photocurable material 114 and the moldstructures 104 a and 104 b. Further the confinement of the photocurablematerial 114 between the mold structures 104 a and 104 b can becontrolled by dispensing a metered volume of the photocurable material114 (e.g., corresponding to the volume between the first area 1202 a andthe second area 1202 b). The photocurable material 114 is then cured(e.g., by irradiating the photocurable material 114 with light 1204suitable for photocuring the photocurable material 114), forming apolymer product 1200 having one or more features defined by the moldstructures 104 a and 104 b.

As shown in the right portion of FIG. 12, after the photocurablematerial 114 has been cured, the mold structures 104 a and 104 b aremoved away from each other (e.g., by moving the actuable stages 102 aand/or 102 b). The polymer product 1200 is then extracted (e.g., asshown in the lower middle portion of FIG. 12).

As described above, the first area 1202 a and second area 1202 b eachcorrespond to the predetermined size and shape of the polymer product1200. Accordingly, the polymer product 1200 is produced without the needto perform a separate singulation process. In some cases, afterextraction, the polymer product 1200 can be directly used in othermanufacturing processes (e.g., incorporated into an apparatus, such as aheadset).

As described above, photocurable material 114 can be dispensed onto themold structures 104 a and/or 104 b according to different patterns.Several example patterns are shown in FIGS. 13A-13E. For ease ofillustration, only a single mold structure 104 b is shown in FIG.13A-13C. However, it is understood that photocurable material 114 can bedispensed into spaces on or adjacent of the mold structure 104 a, themold structure 104 b, or both.

As shown in FIG. 13A, photocurable material 114 can be dispensedaccording to one or more lines. In practice, the number and arrangementof lines can vary. For example, photocurable material 114 can bedispensed according to one, two, three, or more lines. Further, eachline can extend horizontally, vertically, or according to an angle. Insome cases, lines can be eventually distributed along a mold structure(e.g., spaced evenly from one another). In some cases, lines can bedistributed according to some other pattern (e.g., spaced unevenly fromone another). In some cases, each of the lines can have a similarthickness and/or length. In some cases, one or more of the lines candiffer with respect to thickness and/or length. Further, lines need notbe straight. For example, one or more lines can be curved or arced.Further, in some cases, two or more lines can overlap one another.

As shown in FIG. 13B, photocurable material 114 also can be dispensedaccording to one or more drops (e.g., substantially ovular or circulardeposits). In practice, the number and arrangement of dots can vary. Forexample, photocurable material 114 can be dispensed according to one,two, three, or more drops. In some cases, dots can be eventuallydistributed along a mold structure (e.g., spaced evenly from oneanother). In some cases, drops can be distributed according to someother pattern (e.g., spaced unevenly from one another). In some cases,each of the drops can have a similar size and/or shape. In some cases,one or more of the drops can differ with respect to size and/or shape.Further, in some cases, two or more drops can overlap one another.

As shown in FIG. 13C, photocurable material 114 also can be dispensedaccording to other patterns, such as a free form pattern. In practice, afree form pattern can vary. For example, photocurable material 114 canbe dispensed at one, two, three, or more discrete locations. Further,the size and shape of each free form pattern can vary. Further, in somecases, two or more free form patterns can overlap one another.

Although lines, drops, and free form patterns are shown separately withrespect to FIGS. 13A-13C, in some cases, photocurable material 114 alsocan be dispensed according to one or more of lines, drops, and/or freeform patterns in combination with respect to a particular moldstructure.

Further, in some cases, the dispense pattern of the photocurablematerial 114 can correspond to one or more localized features along theareas 1202 a and/or 1202 b. For example, if areas 1202 a and/or 1202 bdefine a feature having a relatively larger volume at a particularlocation (e.g., defining a thicker portion of the polymer product), thedispense pattern can include more photocurable material 114 at thatlocation. As another example, if areas 1202 a and/or 1202 b define afeature having a relatively smaller volume at a particular location(e.g., defining a thinner portion of the polymer product), the dispensepattern can include less photocurable material 114 at that location.

In some cases, the total volume of dispensed photocurable material 114can be precisely metered or regulated, such that the photocurablematerial 114 evenly spreads across the areas 1202 a and 1202 b, withoutsubstantially leaking beyond the areas 1202 a and/or 1202 b. This can beuseful, for example, in reducing or eliminating material waste. Further,this improves the consistency of the resulting polymer product (e.g.,the polymer product need not be cut or trimmed to remove excessphotocurable material that has cured beyond the areas 1202 a and/or 1202b). In some cases, the total volume of dispensed photocurable material114 can be substantially equal to the volume between the areas 1202 and1202 b when the mold structures 104 a and 104 b and aligned.

In some cases, photocurable material 114 can be dispensed between themold structures 104 a and 104 b after the mold structures 104 a and 104b have already been aligned. As an example, FIG. 13D shows two moldstructures 104 a and 104 b in alignment. Photocurable material 114 isdispensed between the mold structures 104 a and 104 b by injecting thephotocurable material 114 at one or more locations 1302 a-e along thesides of the mold structures 104 a and 104 b. The injected photocurablematerial 114 spreads between the mold structures 104 a and 104 b throughcapillary action. In some cases, different amounts of photocurablematerial 114 can be injected at different locations along the sides ofthe mold structures 104 a and 104 b to facilitate uniform spreading.Although five locations 1302 a-e are shown in FIG. 13D, these are merelyillustrative examples. In practice, photocurable material 114 can beinjected at one or more other locations, either instead of or inaddition to those shown in FIG. 13D.

In some cases, one or more of the edges between the mold structures 104a and 104 b can be sealed to restrict the flow of injected photocurablematerial 114. For example, FIG. 13E shows two mold structures 104 a and104 b in alignment. The edges 1304 a-e are sealed (e.g., the moldstructures 104 a and 104 b are joined together along these edges), whilethe edge 1304 f is open and exposed (e.g., the mold structures 104 a and104 remain separate along this edge). The photocurable material 114 canbe injected along the edge 1304 f to fill the volume between the moldstructures 104 a and 104 b. In this configuration, the mold structures104 a and 104 b can be arranged vertically, such that the exposed edge1304 f is positioned along the top of the mold structures 104 a and 104b (e.g., to prevent the photocurable material 114 from pouring out). Thephotocurable material 114 can be cured by directing light horizontally(e.g., through the mold structures 104 a and/or 104 b) instead ofvertically (e.g., as shown in FIG. 1). Further, in some cases, edges canbe reversibly sealed (e.g., using peelable glue or tape). Further still,one or more sealed edges can be exposed before or during the curingprocess (e.g., to remove excess materials and/or to release any stressesdeveloped during the curing process). Although an example arrangement ofsealed and exposed edges are shown in FIG. 13E, this is merely anillustrative example. In practice, another arrangements of sealed andexposed edges are also possible, depending on the implementation.

As described above, spacer structures can be used to regulate thespacing between the mold structures 104 a and 104 b. Spacer structurescan be useful, for example, to control the relative orientation of themold surfaces, such that the resulting polymer products are less likelyto deviate from their intended shape. Further, the resulting polymerproducts are less likely to become distorted (e.g., wrinkled, stretched,or compressed) during production.

In some cases, the spacer structures can be placed beyond the areas 1202a and 1202 b of the mold structures 104 a and 104 b, such that thephotocurable material 114 does not come into contact with the spacerstructures during the production process. This can be beneficial, forexample, in improving the quality of polymer product (e.g., by reducingunintended variation due to interference between the spacer structuresand the photocurable material 114).

As an example, FIG. 14 shows a mold structure 104 b having a surface 120b. The surface 120 b includes a discrete, continuous area 1202 bcorresponding to the predetermined size and shape of a polymer product(e.g., as described with respect to FIG. 12). In this example, the moldstructure 104 b also includes several protrusions 1402 a-d extendingbeyond the periphery of the area 1202 b. Each protrusion 1402 a-dincludes a respective spacer structure 1404 a-d and a respectivefiducial feature 1406 a-d.

The spacer structures 1404 a-d can be similar to those described withrespect to FIGS. 1 and 2. For example, the spacer structures 1404 a-dcan that project from the mold structure 104 b and towards an opposingmold structure (e.g., the mold structure 104 a). Further, the spacerstructures 1404 a-d can each have a substantially equal vertical height,such that when the mold structures 104 a and 104 b are brought together(e.g., pressed together), the spacer structures 1404 a-d abut the moldstructures 104 a and 104 b and a substantially flat gap volume isdefined between them. Further, as the spacer structures 1404 a-d arepositioned beyond the area 1202 b, they are less likely to come intocontact with photocurable material 114 during the production process.Thus, the resulting polymer products are less likely to becomedistorted.

The fiducial features 1406 a-d are structures or markings that can beused to align the mold structure 104 b with the mold structure 104 a.For example, the fiducial features 1406 a-d can include one or morevisually distinctive structures (e.g., contrasting structural patterns)or markings (e.g., contrasting patterns and/or colors indicated by ink,paint, layers, etc.) that enable the system 100 to detect the spatiallocation and/or orientation of the mold structure 104 b (e.g., using avisual registration system, such as one including or more cameras oroptical sensors). Based on this information, the system 100 canmanipulate the mold structure 104 b to control the relative position andorientation between the mold structure 104 a and the mold structure 104b.

As shown in FIG. 14, each of the protrusions 1402 a-d include a platform1408 a-d (upon which the spacer structures 1404 a-d and the fiducialfeatures 1406 a-d are positioned), and a bridge 1410 a-d extendingbetween the platform 1408 a-d and the area 1202 b. The width of thebridge 1410 a-d is narrower than the width of the platform 1408 a-d(e.g., on the plane of the area 1202 b). This is beneficial, forexample, as it further isolates the spacer structures 1404 a-d from thephotocurable material 114 in the area 1202 b. For example, compared to awider bridge, a narrower bridge better restricts the flow ofphotocurable material across it.

Although FIG. 14 only shows a single mold structure 104 b, it isunderstood that the mold structure 104 a can also include one or morefeatures similar to those shown in FIG. 14 (e.g., protrusions, spacerstructures, fiducial features, etc.). Further, although FIG. 14 shows aparticular number of each type of feature and particular locations forthese features, these are merely illustrative examples. In practice, thenumber of each type of feature and/or the locations for each feature candiffer, depending on the implementation.

In some cases, a mold structure can include chemical and/or structuralfeatures that restrict the flow of photocurable material beyond the areacorresponding to the defined size and shape of the polymer product. Thiscan be useful, for example, in reducing or eliminating material waste.Further, this improves the consistency of the resulting polymer product(e.g., the polymer product need not be cut or trimmed to remove excessphotocurable material that has cured beyond the area).

As an example, FIG. 15 shows a mold structure 104 b. The mold structureshown in FIG. 15 can be similar to that shown in FIG. 14. For example,the mold structure 104 b includes a surface 120 b having a discrete,continuous area 1202 b corresponding to the predetermined size and shapeof a polymer product. The mold structure 104 b also includes severalprotrusions 1402 a-d extending beyond the periphery of the area 1202 b.In some cases, each protrusion 1402 a-d can include a respective spacerstructure and/or a respective fiducial feature (omitted for ease ofillustration). In some cases, the mold structure 104 b can include onmore other fiducial features (e.g., fiducial features 1502 a-fpositioned along the area 1202 b).

In this example, the periphery 1500 of the area 1202 b has a surfacechemistry that is different from that of the area 1202 b itself (e.g.,such that a surface energy of a photocurable material is different atthe periphery 1500 compared to the area 1202 b). As an example, theperiphery 1500 can have as surface chemistry that repels thephotocurable material 114 (e.g., to a greater degree than the area 1202b), such that the photocurable material 114 within the area 1202 b isless likely to flow beyond the periphery 1500. This can be useful, forexample, in containing the photocurable material within the area 1202 bduring the production process. In some cases, the periphery 1500 canextend along the edges of the area 1202 b (e.g., the edges of the moldstructure 104 b).

In some cases, the periphery 1500 can be coated with a material thatrepels the photocurable material 114, and/or a hydrophobic material(e.g., a material that has nanostructures on its surface) to serve as“self-cleaning” surfaces for repelling photocurable material 114.Example materials include organically modified silica,poly-dimethyl-siloxane (PDMS), fluoro-silane, and Teflon based coatings.

The width of the periphery 1500 (e.g., the width of the repellant edgeportions) can vary. For example, the width can be less than 0.5 mm, lessthan mm, less than 5 mm, or some other thickness.

Although FIG. 15 only shows a single mold structure 104 b, it isunderstood that the mold structure 104 a can also include one or morefeatures similar to those shown in FIG. 15 (e.g., one or more portionshaving a surface chemistry that repels photocurable material). Further,although FIG. 15 shows a particular number of each type of feature andparticular locations for these features, these are merely illustrativeexamples. In practice, the number of each type of feature and/or thelocations for each feature can differ, depending on the implementation.

In some cases, one or more other portions of the mold structure 104 balso can have a surface chemistry that repels the photocurable material114. For example, one or more of the bridges 1410 a-d and/or platforms1408 a-d can be coated with PDMS, fluorosilane, Teflon, and/or ahydrophobic material to isolate the protrusions 1402 a-d from thephotocurable material 114.

As another example, FIG. 16A shows a mold structure 104 b. The moldstructure shown in FIG. 16A can be similar to that shown in FIG. 14. Forexample, the mold structure 104 b includes a surface 120 b having adiscrete, continuous area 1202 b corresponding to the predetermined sizeand shape of a polymer product. The mold structure 104 b can alsoinclude several protrusions extending beyond the periphery of the area1202 b, each having respective spacer structures and/or fiducialfeatures (omitted for ease of illustration).

In this example, the periphery 1600 of the area 1202 b has a structuralpattern that is different from that of the area 1202 b itself (e.g.,such that a surface energy of a photocurable material is different atthe periphery 1600 compared to the area 1202 b). As an example, theperiphery 1600 can have an etched grating pattern that impedes the flowof photocurable material 114 across it (e.g., compared to the area 1202b), such that the photocurable material 114 within the area 1202 b isless likely to flow beyond the periphery 1600. This can be useful, forexample, in containing the photocurable material within the area 1202 bduring the production process. Further, a patterned periphery 1600 canbe beneficial when producing an optical polymer product. For example, apatterned periphery 1600 on an eyepiece can facilitate the out couplingof stray light within the eyepiece (e.g., stray light propagatingthrough channels other than the desired light propagation channel),thereby improve the quality of images projected by the eyepiece. In somecases, the patterned periphery 1600 can also facilitate the applicationof a light absorbing material (e.g., a carbon black paint) along theedge of the optical polymer product (e.g., to aid in the absorption ofstray light along the edges of an optical polymer product). In somecases, the periphery 1600 can extend along the edges of the area 1202 b(e.g., the edges of the mold structure 104 b).

In some cases, the structural pattern of the periphery 1600 can beconfigured to have a particular volume (e.g., within its channels). Thiscan be useful, for example, as it enables the periphery 1600 to acceptup to a particular volume of photocurable material, such that thephotocurable material does not flow beyond it. In some cases, the volumedefined by the periphery) 1600 can be greater than the expected material“overfill” of the mold (e.g., the difference between the volume ofphotocurable material deposited into the area 1202 b and the availablevolume of between areas 1202 a and 302 b after the mold structure 104 aand 104 b are aligned).

In some case, the structural pattern of the periphery 1600 can beconfigured to impart brittle or breakable features on the resultingpolymer product (e.g., a relatively fragile edge that can be broken awayfrom the rest of the polymer product with the application of force).This can be useful, for example, as it facilitates the trimming orexcess material without the need to perform a separate singulationprocess (e.g., laser cutting).

An example etched grating pattern for the periphery 1600 is shown inFIG. 16B. In this example, the pattern includes alternating protrusions1602 and channels 1604. The dimensions of each protrusion and channelcan vary, depending on the implementation. In some cases, the width of aprotrusion w₁ can be between 50 to 200 μm. In some cases, the width of achannel w₂ can be between 50 to 200 μm. In some cases, the height h of aprotrusion (e.g., beyond the level of an adjacent channel) can bebetween 1 to 10 μm. This can be useful, for example, in providing aWenzel surface for “drop pinning” drops of photocurable material to theperiphery 1600 (e.g., such that drops of photocurable material hadadhered to the periphery 1600, and do not flow beyond it). Thedimensions can be differ, for example, to facilitate the capture ofdifferent volumes of photocurable product along the periphery 1600.

In some cases, the periphery 1600 can be patterned with hydrophobicnanostructures. This can be useful, for example, in provide aCassie-Baxter surface to provide a “drop rolling” surface (e.g., suchthat drops of photocurable material roll away from the periphery 1600,thereby delimiting a clear boundary for the area 1202 b. As examples,nanostructures can be replicated from a nano-patterned mold usingmaterials such as organically modified silica, polydimethylsiloxane,fluoro-silane and Teflon. In addition, photocurable materials doped withrelease functionalities can also be used to create such hydrophobicfeatures directly.

In some cases, the protrusions and channels can alternate in a regularrecurring spatial pattern. In some case, the protrusion and channels canand channels can alternate according to some other spatial pattern.

The width of the periphery 1600 (e.g., the width of the patterned edgeportions) can vary. For example, the width can be less than 0.5 mm, lessthan mm, less than 5 mm, or some other thickness.

Although FIGS. 16A and 16B only show a single mold structure 104 b, itis understood that the mold structure 104 a can also include one or morefeatures similar to those shown in FIG. 16A (e.g., one or morestructural patterns for controlling the flow of photocurable material).Further, although FIGS. 16A and 16B show a particular number of eachtype of feature and particular locations for these features, these aremerely illustrative examples. In practice, the number of each type offeature and/or the locations for each feature can differ, depending onthe implementation.

Further, surface chemistry features and structural pattern features aredescribed separately with respect to FIGS. 15, 16A, and 16B show, it isunderstood that a mold structure can have both the described surfacechemistry features and the described structural pattern features.

In some cases, a mold structures can be used to form multiple differentpolymer products concurrently, without the need to perform a separatesingulation process. As an example, FIG. 17 shows an example moldstructure 104 b. In this example, the mold structure 104 b includes asurface 120 b having multiple different discrete, continuous areas 1702a-d, each corresponding to the predetermined size and shape of a polymerproduct. The mold structure 104 b can includes several spacer structures1704 a-e.

Each area 1702 a-d can be similar to the areas 1202 a and/or 1202 bshown and described with respect to FIGS. 12-16. For example, each area1702 a-d can be a continuous area corresponding to the predeterminedsize and shape of a particular polymer product. Further, each area 1702a-d can include a periphery 1706 a-d having a surface chemistry thatrepels the photocurable material (e.g., in a similar manner as describedwith respect to FIG. 15) and/or a periphery 1706 a-d having a structuralpattern that regulates the flow of photocurable material (e.g., “droppinning” or “drop rolling” surfaces).

Further, the area 1708 of the surface 120 b beyond each the areas 1702a-d (e.g., the portion of the surface 120 b that are not used to shapethe polymer products) also can have a surface chemistry that repelsphotocurable material (e.g., coated with PDMS, fluorosilane, and/orTeflon). This can be useful, for example, in restricting the flow ofphotocurable material beyond each of the areas 1702 a-d.

The spacer structures 1704 a-e can be similar to those shown anddescribed with respect to FIGS. 1, 2, and 14. For example, the spacerstructures 1704 a-e can that project from the mold structure 104 b andtowards an opposing mold. Further, the spacer structures 1704 a-e eachhave a substantially equal vertical height, such that when the moldstructure 104 b is brought other with another mold structure, the spacerstructures 1704 a-e abut the mold structures and a substantially flatgap volume is defined between them.

This arrangement is beneficial, for example, as it enables theproduction of multiple polymer products concurrently without the need toperform for a separate singulation process. Although FIG. 17 shows amold structure having four discrete areas for forming polymer products,this is merely an illustrative example. In practice, a mold structurecan have any number of discrete areas for forming polymer products(e.g., one, two, three, four, or more).

Further, although FIG. 17 only shows a single mold structure 104 b, itis understood that the mold structure 104 a can also include one or morefeatures similar to those shown in FIG. 17 (e.g., multiple discreteareas for forming polymer products). Further, although FIG. 17 showsparticular locations for each of its features, these are merelyillustrative examples. In practice, the locations for each feature candiffer, depending on the implementation.

FIG. 18 shows an example process 1800 for producing a polymer product.The process 1800 can be performed, for example, using the systems 100 or900. In some cases, the process 1800 can be used to produce polymerfilms suitable for use in optical applications (e.g., as a part ofwaveguides or eyepieces in an optical imaging system). In some cases,the process 1800 can be used to form polymer products having a thicknessof no more than 1000 μm, an area of at least 1 cm², and a predeterminedshape.

In the process 1800, a first mold portion is provided (step 1802). Thefirst mold portion has a first surface including a discrete, continuousfirst area corresponding to the predetermined shape of the waveguidepart. The first area is bounded by an edge region having a differentsurface chemistry and/or surface structure than the first area.

A second mold portion is also provided (step 1804). The second moldportion has a second surface including a discrete, continuous secondarea corresponding to the predetermined shape of the waveguide part. Thesecond area is bounded by an edge region having a different surfacechemistry and/or surface structure than the second area.

In some cases, the edge region of the first and/or second mold portionsincludes a material that repels the photocurable material. In somecases, the edge region of the first and/or second mold portions includesa patterned surface configured to pin droplets of the photocurablematerial. In some cases, the edge region of the first and/or second moldportions includes a patterned surface configured to roll droplets of thephotocurable material. Example mold portions are shown and described,for example, with respect to FIGS. 1-9 and 12-17. Example edge regionsare shown and described, for example, with respect to FIGS. 15-17.

A metered amount of a photocurable material is dispensed into a spaceadjacent the first area of the first mold portion (step 1806). In somecases, the metered amount of photocurable material is dispensed at aplurality of discrete locations in the space adjacent the first area ofthe first mold portion. In some cases, the metered amount ofphotocurable material is dispensed according to an asymmetric pattern inthe space adjacent the first area of the first mold portion. In somecases, the metered amount of photocurable material is dispensed at aperiphery of the first surface of the first mold portion. Exampledispensing patterns are shown and described, for example, with respectto FIGS. 13A-13E.

The first and second surfaces are arranged opposite each other with thefirst and second areas being registered with respect to each other (step1808). In some cases, the first and second surfaces are arrangedopposite each other prior to dispensing the photocurable material (e.g.,as shown and described with respect to FIGS. 13D and 13E). In somecases, the first and second surfaces are arranged opposite each otherafter dispensing the photocurable material (e.g., as shown and describedwith respect to FIGS. 12 and 13A-13C). In some cases, the first andsecond areas are registered with respect to each other based on one ormore fiducial markings on the first and/or second surfaces. The fiducialmarkings can be located outside of the first and second areas (e.g., asshown and described with respect to FIG. 14).

A relative separation between the first surface and the second surfaceis adjusted so that the photocurable material fills a space betweenfirst and second areas of the first and second surfaces, respectively,having the predetermined shape (step 1810). In this arrangement, thedifferent surface chemistry and/or surface structure between the firstand second areas and their corresponding edge regions prevent flow ofthe photocurable material beyond the edge regions.

In some cases, the relative separation between the first and secondsurfaces is controlled based on one or more spacers located on the firstand/or second surfaces. The one or more spacers can be located outsideof the first and second areas (e.g., as shown and described with respectto FIGS. 14 and 17).

The photocurable material in the space is irradiated with radiationsuitable for photocuring the photocurable material to form a cured filmin the shape of the waveguide part (step 1812). Example techniques forphotocurable the photocurable material are described with respect toFIGS. 1 and 12.

The cured film is separated from the first and second mold portions toprovide the waveguide part (step 1814). In some case, a head mounteddisplay is assembled using the waveguide part.

As described herein, during the casting and curing process, variousfactors can interfere with the shape of the resulting film, causing itto become distorted from its intended shape. As an example, a film canbecome distorted due to the build up of internal stresses within duringthe polymerization process. For instance, as a photocurable material iscured, monomers of the photocurable material polymerize into longer andheavier chains. Correspondingly, the photocurable material reduces involume (e.g., experiences “shrinkage”) as the polymer chains physicallymove together. This results in a build up to internal stresses inside ofthe photocurable material (e.g., stresses resulting from an impedance topolymer chain mobility), and a storage of strain energy within thephotocurable material. When the cured film is extracted from the mold,the strain energy is released resulting in thinning of the film. Thefilm can thin differently depending on the spatial distribution of theinternal stresses. Thus, films may exhibit variations from film to film,depending on the particular spatial distribution of internal stressesthat were introduced during the polymerization process. Accordingly, theconsistency of a film can be improved by regulating the distribution ofstress within the film during the casting process.

To illustrate, FIG. 19A shows an example polymer film 1900 during thecasting and curing process (e.g., when the polymer film 1900 ispositioned between mold structures 104 a and 104 b), and FIG. 19B showsthe polymer film 1900 after curing and extraction (e.g., after thepolymer film 1900 has been “demolded”). As shown in FIG. 19A, as thepolymer film 1900 is cured, it shrinks in size (indicated by thevertical arrows). This can result in a delamination of the polymer film1900 from the mold structures 104 a and/or 104 b (e.g., if the stress isgreater than the adhesion or bond force between the polymer film and themold structure). Further, this can cause the mold structure 104 b tobecome separated from the vacuum chuck 1902 holding the mold structure104 b in place (e.g., if the stress is greater than the vacuum strengthof the vacuum chuck 1902). Further still, this can cause a fracturingthe in the mold structures 104 a and 104 b (e.g., if the stress isgreater than the strength of the mold structures). Further still, thisshrinkage can result in the storage of strain energy within the polymerfilm 1900. As shown in FIG. 19B, after the polymer film 1900 isextracted from the mold structures 104 a and 104 b, it experiencesstructural relaxation and further shrinking (indicated by the verticalarrows), resulting in a thinning of the polymer film 1900.

The polymer film can thin differently depending on the spatialdistribution of the internal stresses, resulting in localized variationsin thickness. In some cases, the thickness variation distribution iscorrelated to the intensity distribution of the light used to photocurethe photocurable material.

As an example, FIG. 20 shows an example intensity distribution of light2000 used to photocure the photocurable material (e.g., light generatedusing a 2×2 array of ultraviolet (UV) light sources with overlappingareas). Portions of the distribution having a higher intensity of lightare shown in darker shades, while portions having a lower intensity oflight are shown in lighter shades. FIGS. 21A and 21B show two examplepolymer films 2100 a and 2100 b that were cured using the light havingthe intensity distribution 2000. As shown in FIG. 21A and 21B, each ofthe polymer films 2100 a and 2100 b exhibits wrinkling and markedthickness variation, particularly at its fringes.

Various techniques can be used to regulate the internal stresses withina polymer film before, during, and/or after the curing process.

In some cases, the mold structures 104 a and 104 b can be adjustedduring the curing process to compensate for shrinkage in thephotocurable material. An example, FIG. 22A shows photocurable material114 positioned between the mold structures 104 a and 104 b. In thisexample, the mold structure 104 b is fixed in position (e.g., secured toa vacuum chuck 1902), while the mold structure 104 a is configured tomove up and down (e.g., moved away from the mold structure 104 a, andtowards the mold structure 104 b using an actuable stage). Further, themold structures 104 a and 104 b are positioned such that they apply aparticular amount of force onto the photocurable material 114.

During the curing process, light is directed towards the photocurablematerial 114. As the photocurable material 114 cures and shrinks in size(e.g., reduces in thickness), the mold structure 104 a is moved towardsthe mold structure 104 b to compensate for the change in size and tomaintain the same amount of force on the photocurable material 114. Thisreduces or otherwise eliminates the build up of internal stresses withinthe photocurable material, and reduces the potential thicknessvariations in the photocurable material 114 after it is cured andextracted from the mold.

In some cases, the mold structures 104 a and 104 b can apply acompression force to the photocurable material 114 while thephotocurable material 114 is still in a “reflowable” liquid phase (e.g.,before the photocurable material 114 been cured to its gel point). Insome cases, the mold structures 104 a and 104 b can apply a compressionforce to the photocurable material 114 while photocurable material 114is in a compressible gel phase (e.g., after the photocurable material114 has been cured to its gel point, but before it has reached its solidpoint).

In some cases, the mold structures 104 a and 104 b can be operatedaccording to a closed loop control system. For example, as shown in FIG.22A, the mold structures 104 a and 104 b can include one or more sensorassemblies 122 including force sensors, each configured to measure anapplied force at a particular location along a particular mold structure104 a or 104 b. The sensor assemblies 122 can be communicatively coupledto the control module 110 (e.g., as shown and described with respect toFIG. 1), and can be configured to transmit force measurements to thecontrol module 110 during operation of the system. Based on the forcemeasurements, the control module 110 can control the position of themold structure 104 a relative to the mold structure 104 b (e.g., usingthe actuable stage 102 a) to maintain a constant force on thephotocurable material 114 during the curing process, while maintainingparallelism between the mold structure 104 a and the mold structure 104b. The final thickness of the resulting polymer film and the stresslevel stored in the polymer film can be controlled by regulating theapplied force on the photocurable material 114. In some cases, forces inthe range of 5 N to 100 N can be applied to the photocurable material114. In some cases, applying a higher force enables the final thicknessof the polymer film to be closer to the width of the initial gap betweenthe mold structures 104 a and 104 b, but with less regulation of stresswithin the polymer film.

In some cases, the mold structures 104 a and 104 b can be operatedaccording to an open loop control system. For example, as shown in FIG.22B, the mold structures 104 a and 104 b can include one or morecompressible spacer structures 6222, and one or more incompressiblespacer structures 2204. The incompressible spacer structures 2204 definethe minimum distance between the mold structures 104 a and 104 b. Thecompressible spacer structures 2202 have a greater height than theincompressible spacer structures 2204, and are less stiff than theincompressible spacer structures 2204 (e.g., such that they can becompressed by the application of a certain amount of force). Duringoperation of the system, the control module 110 moves the mold structure104 a towards the mold structure 104 b to compress the compressiblespacer structures 2204, and corresponding to apply a predeterminedconstant force to the photocurable material 114). The control module 110continues to move the mold structure 104 a towards the mold structure104 b until they are abutted by the incompressible spacer structures2204.

Each of the compressible spacer structures 2204 can have the same heightand the same stiffness, such that the mold structures 104 a and 104 bapply an even force onto the photocurable material 114 while maintainingparallelism between the mold structure 104 a and the mold structure 104b. The final thickness of the resulting polymer film and the stresslevel stored in the polymer film can be controlled by specifyingparticular heights and stiffnesses for the compressible spacerstructures 2204. In some cases, the height of a compressible spacerstructure 2204 can be between 5% to 15% greater than the height of thecompressive spacer structures 2204 (e.g., corresponding to the volumeshrinkage of the photocurable material 114 during the curing process).In some cases, the stiffness of the compressible spacer structures canbe between 0.01 GPa and 0.1 GPa (e.g., similar to rubber). In somecases, the compressible spacer structures 2204 can be constructed ofrubber, polyethylene, Teflon, polystyrene foam, and/or othercompressible material.

In some cases, the system can also include one or more spring mechanisms2206 positioned between the mold structures 104 a and 104 b. Thesespring mechanisms 2206 can further regulate the amount of force that isapplied to the photocurable material 114, and to further maintain theparallelism between the mold structure 104 a and the mold structure 104b

In some cases, the mold structures 104 a and 104 b can be cyclicallymoves towards each other and away from each other to apply a cyclic loadon the photocurable material 114 during the curing process. This can beuseful, for example, as compressing and stretching during thephotocurable material 114 during the curing process can relax thestresses build into the photocurable material.

As an example, as shown in FIG. 23, the mold structure 104 a can bemoved according to one or more movement patterns 2300 a-c. As anexample, in the movement pattern 2300 a, the mold structure 104 a ismoved according to a low response time and low gain (e.g., the moldstructure 104 a is moved towards the mold structure 104 b after thephotocurable material 114 has been cured to its gel point, and graduallymoved away). As another example, in the movement pattern 2300 b, themold structure 104 a is moved according to a high response time and highgain (e.g., the mold structure 104 a is alternatively moved away fromthe mold structure 104 b and towards the mold structure in according toan “overshoot” decaying oscillatory pattern after the photocurablematerial 114 has been cured to its gel point). As another example, thein the movement pattern 2300 c, the mold structure 104 a is movedaccording to a medium response time and medium gain (e.g., the moldstructure 104 a is alternatively moved away from the mold structure 104b and towards the mold structure according to a “tuned” decayingoscillatory pattern after the photocurable material 114 has been curedto its gel point). Although three example patterns are shown in FIG. 23,other patterns are also possible, depending on the implementation.

In practice, the mold structures 104 a and 104 b can be controlled suchthat the spacing between them oscillates or “bounces” a particularnumber of times, and does so according to a particular frequency. As anexample, the spacing between the mold structures 104 a and 104 b canoscillate one or more times (e.g., one, two, three, or more times)between the gel point and the solid point. In some cases, the length oftime between a gel point and the solid point can be approximately threeseconds. This can correspond to oscillations of 0.33 Hz, 0.67 Hz, 1 Hz,or more. Further, the amplitude of the oscillations can also vary. Insome cases, the each oscillation can be between approximately 5 to 10 μmupward or downward relative to a central reference position 702

In some cases, built in stresses can be removed from a polymer film byannealing the polymer film before it is extracted from the mold (e.g.,before “demolding” the polymer film). Various techniques can be used toapply heat to a polymer film while it is still between the moldstructures. As examples, a polymer film can be heated through conductionheating and/or and radiation heating, such as using one or more heatedchucks, high intensity lamps, infrared (IR) lamps, and/or microwaves. Insome cases, radiation heating may be preferable (e.g., for fasterprocess time and potentially selective heating of the polymer filmonly). In some cases, the polymer film can be annealed by heating it to40° C. to 200° C. for a period of 10 seconds to 3 minutes.

In some cases, the photocurable material 114 can be cured using patternsof light having a particular spatial distribution and/or particulartemporal characteristics to reduce built in stresses from the resultingpolymer film. Example lighting patterns 800 a-c are shown in FIGS.24A-24C.

As shown in FIG. 24A, photocurable material can be cured by irradiatingthe photocurable material with a lighting pattern 2400 a having acontinuous and uniform intensity over a period of time (e.g., from thebeginning of the curing process 2402 until the end of the curing process2404 when the photocurable material is fully cured). In some cases, useof the light pattern 2400 a can result in a polymer product 2406 ahaving a significant amount of built up stress (e.g., the non-stopexposure can impair the ability of the polymer material to respondquickly to movements by the polymer chains during shrinkage). In somecases, this can result in a polymer product 2406 a that is thicker alongits periphery than along its central region (e.g., when viewed along across-section along the y-z plane).

As shown in FIG. 24B, photocurable material can be cured by irradiatingthe photocurable material with a lighting pattern 2400 b having avariable intensity over time. Initially (e.g., at the beginning of thecuring process 2402), the photocurable material is irradiated by highintensity light. As the curing process progresses, the photocurablematerial is irradiated by lower and lower intensity light until thephotocurable material is fully cured (e.g., until the end of the curingprocess 2404). In some cases, use of the light pattern 2400 b can resultin photocurable material absorbing a relatively large amount of light inthe initial stages of the curing process, resulting in creation ofenough free radicals to drive the polymerization reactions. As theintensity of the light decreases, the polymer chains can re-arrangeslowly, resulting in relatively lower amounts of stress in thecross-linked network (e.g., compared to the use of the lighting pattern2400 a). In some cases, this can result in a polymer product 2406 bbetter mechanical properties (e.g., higher Young's modulus and/orhardness) and more consistent spatial dimensions (e.g., lower TTV)compared to use of the lighting pattern 800 a.

As shown in FIG. 24C, photocurable material can be cured by irradiatingthe photocurable material with another lighting pattern 2400 c having avariable intensity over time. Initially (e.g., at the beginning of thecuring process 2402), the photocurable material is irradiated by lowerintensity light. As the curing process progresses, the photocurablematerial is irradiated by higher and higher intensity light until thephotocurable material is fully cured (e.g., until the end of the curingprocess 2404). In some cases, use of the light pattern 2400 c can resultin photocurable material absorbing a relatively lower amount of light inthe initial stages of the curing process, resulting in lower rates ofreactions during the early stages of the curing process. Thus, themonomers of the photocurable material react more slowly, resulting inrelatively lower stress built up in the network. Subsequently, higherintensity light can be used to cure the photocurable material fully. Insome cases, this can result in more consistent spatial dimensions (e.g.,lower TTV) compared to use of the lighting pattern 2400 a. However, themechanical properties may be less desirable in some contexts (e.g.,compared to use of the lighting pattern 2400 b) due to a relatively slowrate of polymerization.

Although example lighting patterns 2400 a-c are shown and describedabove, these are merely illustrative examples. In practice, otherlighting patterns can also be used to cure photocurable material, eitherinstead of in in additional to those described herein.

In some cases, photocurable material can be cured by irradiating thephotocurable material with one or more pulses of light over a period oftime (e.g., exposing the photocurable material to light according to oneor more on and off cycles). In some cases, the duration of each pulse ofradiation (e.g., the duration of each “on” state) can vary relative tothe duration of each period of time between pulses (e.g., the durationof each “off” state). Example lighting patterns 2500 a-c are shown inFIG. 25.

As shown in FIG. 25A, photocurable material can be cured by irradiatingthe photocurable material with a lighting pattern 2500 a having multiplepulses over a period of time. In this example, the duration of eachpulse t_(on) (e.g., duration of each “on” state) is equal to theduration between pulses t_(off) (e.g., the duration of each “off”state), corresponding to a 50% duty cycle of light. The light pattern2500 a can be used to cure a photocurable material having a moderaterate of polymerization (e.g., during the “on” stages), while allowingthe photocurable material to cool during the curing process (e.g.,during the “off” stages). This can be beneficial, for example, incontrolling the amount of heat and/or stress in the photocurablematerial. Further, the physical properties of the resulting polymerproduct (e.g., TTV patterns of the polymer product) can be realized byselecting a particular time interval for t_(on) and t_(off). In somecases, t_(off) and t_(on) can be between 0.05 s and 5 s.

As shown in FIG. 25, photocurable material also can be cured byirradiating the photocurable material with another lighting pattern 2500b having multiple pulses over a period of time. In this example, theduration of each pulse t_(on) (e.g., duration of each “on” state) isgreater than the duration between pulses t_(off) (e.g., the duration ofeach “off” state), corresponding to a greater than 50% duty cycle oflight. The light pattern 2500 b can be used to cure a photocurablematerial having a slower rate of polymerization (e.g., by applying morelight during the “on” stages compared to the lighting pattern 2500 a todrive polymerization), while also allowing the photocurable material tocool during the curing process (e.g., during the “off” stages). Asabove, this can be beneficial in controlling the amount of heat and/orstress in the photocurable material. Further, the physical properties ofthe resulting polymer product (e.g., TTV patterns of the polymerproduct) can be realized by selecting a particular time interval fort_(on) and t_(off). In some cases, t_(off) can be between 0.05 s and 5s, and t_(on) can be between 0.05 s and 5 s.

As shown in FIG. 25, photocurable material also can be cured byirradiating the photocurable material with another lighting pattern 2500c having multiple pulses over a period of time. In this example, theduration of each pulse t_(on) (e.g., duration of each “on” state) isless than the duration between pulses t_(off) (e.g., the duration ofeach “off” state), corresponding to a less than 50% duty cycle of light.The light pattern 2500 c can be used to cure a photocurable materialhaving a faster rate of polymerization (e.g., by applying less lightduring the “on” stages compared to the lighting pattern 2500 a to drivepolymerization), while also allowing the photocurable material to coolduring the curing process (e.g., during the “off” stages). As above,this can be beneficial in controlling the amount of heat and/or stressin the photocurable material. Further, the physical properties of theresulting polymer product (e.g., TTV patterns of the polymer product)can be realized by selecting a particular time interval for t_(on) andt_(off). In some cases, t_(off) can be between 0.05 s and 5 s, andt_(on) can be between 0.05 s and 5 s.

In some cases, the intensity of one or more pulses of radiation can havea different intensity from or more other pulses of radiation. Examplelighting patterns 2600 a-c are shown in FIG. 26. In each of theseexamples, the pulses of radiation alternate between pulses having ahigher intensity and pulses having a lower intensity. This can beuseful, for example, as some photocurable materials have lower thermalconductivity, and the heat generated by UV light and/or exothermicprocesses will take longer time to dissipate by conduction. Alternatinghigh and low intensity pulses can help maintain the curing reaction atsmoother rate. Although the patterns 2600 a-c shown in FIG. 26 alternatebetween pulses having two different intensities, these are merelyillustrative examples. In some cases, patterns can alternative betweenpulses having three or more different intensities (e.g., three, four,five, or more). Further, in some cases, patterns do not alternatebetween pulses having different intensities according to a regular orrepeating pattern. For example, patterns can include pulses having anycombination of intensities and arranged in any order.

In practice, the frequency of pulses can different, depending on theimplementation. As an example, the frequency of pulses can be between0.1 Hz and 20 Hz. In some cases, the frequency of pulses can beconstant. In some cases, the frequency of pulses can vary over time.

In some cases, photocurable material can be cured by irradiating thephotocurable material with light that varies in intensity with respectto space. For example, certain portions of the photocurable material canbe irradiated with higher intensity light, while other portions of thephotocurable material can be irradiated with lower intensity light. Thiscan be useful, for example, in controlling the rate of polymerizationphotocurable material in localized areas to regulate the built up ofheat and/or stress.

As an example, FIG. 27A shows a lighting pattern 2700 that varies withrespect to space (viewed from the x-y plane). Lighter shadescorresponding to lower light intensity, while darker shades correspondto higher light intensity. A cross-sectional profile 2702 of thelighting pattern (e.g., along the x direction). In this example, thelighting pattern 2700 irradiates a central portion 2702 with lowerintensity light, while irradiating peripheral portions 2704 with higherintensity light (e.g., according to a curved profile pattern). This canbe beneficial, as a polymer film often accumulates more stress at itscenter than along its edges (e.g., due to the lack of surroundingreflowable polymer material to compensate for the shrinkage).Accordingly, exposing the central portion of the polymer film to lessintense light compared to its edges (e.g., to slow the rate ofpolymerization) can reduce the amount of accumulated stress, and improvethe consistency of the polymer film. Although an example pattern isshown in FIG. 27A, this is merely an illustrative example. In practice,a lighting pattern can have different spatial patterns, depending on theimplementation.

Further, in some cases, photocurable material can be cured byirradiating different portions of the photocurable material with lightin sequence. For example, certain portions of the photocurable materialcan be irradiated with light first, followed by other portions of thephotocurable material. This can be useful, for example, in controllingthe rate of polymerization photocurable material in localized areas inparticular sequence to regulate the built up of heat and/or stress.

As an example, FIG. 27B shows a lighting pattern 2750 having five zones2752 a-e arranged in a concentric pattern. In this example, aphotocurable material can be cured by first irradiating the photocurablematerial using along a central portion 2752 a, then along the ringportion 2752 b, then along the ring portion 2752 c, then along the ringportion 2752 d, and finally along the ring portion 2752 e in a sequence(e.g., such that a center of the photocurable material is cured first,and the edges of the photocurable material are cured last). This isbeneficial, for example, as provides lateral shrinkage compensation(e.g., along the x-y plane) through the surrounding reflowable polymermaterial. A sequential pattern of radiation can be achieved, forexample, using individually addressable light source arrays (e.g., oneor more arrays of light emitting diodes), UV optics, grey-scale UVwindows, UV masks, iris shutters, among others. Although an examplepattern is shown in FIG. 27B, this is merely an illustrative example. Inpractice, a lighting pattern can include any number of different zonesthat are illuminated in any order during the casting process.

Further, although several different techniques are shown and describedabove, these techniques is not mutually exclusive. In practice, anynumber of these techniques can be used in conjunction to regulate thebuild up of stress in a polymer product to improve the consistency ofthe polymer product. As an example, a polymer product can be produced bycontrolling the relative space between molds structures before, during,and after casting (e.g., as described with respect to FIGS. 22A, 22B,and 23), irradiating photocurable material according to lightingpatterns having different spatial and/or distributions and/or temporalcharacteristics (e.g., as described with respect to FIGS. 24A-24C, 25,26, 27A, and 27B), either individually or in any combination.

Further, one or more of these techniques can be used to produce polymerproducts having particular shapes. As examples, several differentpolymer products 2800 are shown in cross section in FIGS. 28A and 28B.For instance, as shown in FIG. 28A, polymer products 2800 can haveasymmetric configurations or asymmetric configurations. In some cases, apolymer product 2800 can have one or more convex surfaces. In somecases, a polymer product 2800 can have one or more concave surfaces.Further, as shown in FIG. 28B, a polymer product 2800 can have a centraleyepiece area 2802 (e.g., an optical portion to receive and transmitlight), and a support portion 2804 (e.g., a radially peripheral portionproviding structural support for the eyepiece area). These arrangementscan be achieved using one or more of the technique described herein.

As an example, the polymer product 2800 a can be produced by combiningthe techniques shown and described with respect to FIGS. 27A and 27B.For example, a photocurable material can be initially irradiated (e.g.,with UV light) according to the portions 2752 a-d of the lightingpattern 2750 in conjunction. Further, the spatial distribution of lightintensity can be set according to the lighting pattern 2700 (e.g., suchthat the central portion 2702 of the photocurable material is irradiatedwith lower intensity light, and the peripheral portions 2704 areirradiated with progressively higher intensity light according to acurved profile pattern). This results in a flat central eyepiece area2802. Subsequently, the photocurable material can be irradiated (e.g.,with UV light) according to the portion 2752 e of the lighting pattern2750 (e.g., along the periphery of the polymer product) with asubstantially lower light intensity (e.g., a lower than the lightingintensity of the portions 2752 a-d). This results in a thicker supportportion 2804 along the periphery of the polymer product.

FIG. 29 shows an example process 2900 for forming a waveguide film. Theprocess 2900 can be performed, for example, using the systems 100 or900. In some cases, the process 2900 can be used to produce polymerfilms suitable for use in optical applications (e.g., as a part ofwaveguides or eyepieces in an optical imaging system). In some cases,the process can be particularly useful for producing waveguides oreyepieces suitable for use in a headset. For instance, the process canbe used to produce waveguides or eyepieces having a thickness and/orcross-sectional area that are sufficient to guide light and projectlight covering a field of view of a headset wearer. As an example, theprocess can be used to produce polymer products having a thickness of nomore than 1000 μm (e.g., as measured along the z-axis of a Cartesiancoordinate system), such as 800 μm or less, 600 μm or less, 400 μm orless, 200 μm or less, 100 μm or less, or 50 μm or less, and an area ofat least 1 cm² (e.g., as measured with respect an x-y plane of theCartesian coordinate system), such as 5 cm² or more, 10 cm² or more,such as up to about 100 cm² or less, and having a predetermined shape.In certain cases, the polymer film can have a dimension of at least 1 cm(e.g., 2 cm or more, 5 cm or more, 8 cm or more, 10 cm or more, such asabout 30 cm or less) in at least one direction in the x-y plane. Asanother example, the process can be used to produce polymer productshaving a thickness between 10 μm to 2 mm and an area as large as 1000cm² (e.g., a circular polymer product having a diameter of approximately18 cm.

In the process 2900, a photocurable material is dispensed into a spacebetween a first mold portion and a second mold portion opposite thefirst mold portion (step 2902). Example systems including mold portionsare described, for example, with respect to FIG. 1.

A relative separation between a surface of the first mold portion withrespect to a surface of the second mold portion opposing the surface ofthe first mold portion is adjusted (step 2904). In some cases, therelative separation can be adjusted so that at least a portion the spacefilled with the photocurable material has a predetermined shape. In somecases, the relative separation can be adjusted so that at least aportion the space filled with the photocurable material has a thicknessof no more than 1000 μm, an area of at least 1 cm². In some cases, therelative separation can be adjusted so that at least a portion the spacefilled with the photocurable material has a thickness between 10 μm to 2mm and an area as large as 1000 cm². Example systems for adjusting thepositions of mold portions are described, for example, with respect toFIG. 1.

In some cases, varying the relative separation can include oscillatingthe position of the first mold portion relative to the second moldportion. Example oscillation techniques are described, for example, withrespect to FIG. 23

The photocurable material in the space is irradiated with radiationsuitable for photocuring the photocurable material to form a curedwaveguide film (step 2906). Example systems for irradiating photocurablematerial are described, for example, with respect to FIG. 1.

Concurrent to irradiating the photocurable material, at least one of thefollowing is performed: (i) varying the relative separation between thesurface of the first mold portion and the surface of the second moldportion, and varying an intensity of the radiation irradiating thephotocurable material (step 2908).

In some cases, the relative separation can be varied to regulate a forceexperienced by the first mold portion along an axis extending betweenthe first mold portion and the second mold portion. In some cases, therelative separation can be varied based on a closed-loop control systemthat regulates the force. Example closed loop systems are described, forexample, with respect to FIG. 22A.

In some cases, the relative separation can be varied after irradiatingthe photocurable material for a time sufficient to reach a gel point inthe photocurable material. In some cases, the relative separation can bereduced after irradiating the photocurable material for the timesufficient to reach the gel point in the photocurable material.

In some cases, varying the relative separation can include moving thefirst mold portion towards the second mold portion to compress one ormore spacer structures disposed between the first mold portion and thesecond mold portion. In some cases, the spacer structures can becompressed according to an open-loop control system. Example open loopsystems are described, for example, with respect to FIG. 22B.

In some cases, varying the intensity of the radiation can includevarying a spatial intensity pattern irradiating the photocurablematerial. Example spatial intensity patterns of radiation are described,for example, with respect to FIG. 27A.

In some cases, varying the intensity of the radiation can includevarying a power of the radiation. Varying the power can include pulsingthe radiation. In some cases, each pulse of the radiation can have thesame power. In some cases, pulses of the radiation can have differentpower. In some cases, each pulse of the radiation can have the sameduration. In some cases, pulses of the radiation can have differentdurations. In some cases, a pulse frequency can be constant. In somecases, a pulse frequency can be varied. Example pulse patterns ofradiation are described, for example, with respect to FIGS. 25 and 26.

In some cases, varying the intensity of the radiation can includesequentially irradiating different areas of the space. Examplesequential patterns of radiation are described, for example, withrespect to FIG. 27B.

In some cases, the thickness of the space filled with photocurablematerial varies and the intensity of the radiation can be varied so thatregions of high relative thickness receive a higher radiation dosecompared to regions of low relative thickness.

In some cases, the process can further include separating the curedwaveguide film from the first mold portion and the second mold portion.

In some cases, the process can include assembling a head mounted displaycomprising the waveguide film formed using the process described herein.

Some implementations of subject matter and operations described in thisspecification can be implemented in digital electronic circuitry, or incomputer software, firmware, or hardware, including the structuresdisclosed in this specification and their structural equivalents, or incombinations of one or more of them. For example, in someimplementations, the control module 110 can be implemented using digitalelectronic circuitry, or in computer software, firmware, or hardware, orin combinations of one or more of them. In another example, theprocesses 1100, 1800, and 2900 shown in FIGS. 11, 18, and 29,respectively, can be implemented, at least in part, using digitalelectronic circuitry, or in computer software, firmware, or hardware, orin combinations of one or more of them.

Some implementations described in this specification can be implementedas one or more groups or modules of digital electronic circuitry,computer software, firmware, or hardware, or in combinations of one ormore of them. Although different modules can be used, each module neednot be distinct, and multiple modules can be implemented on the samedigital electronic circuitry, computer software, firmware, or hardware,or combination thereof

Some implementations described in this specification can be implementedas one or more computer programs, i.e., one or more modules of computerprogram instructions, encoded on computer storage medium for executionby, or to control the operation of, data processing apparatus. Acomputer storage medium can be, or can be included in, acomputer-readable storage device, a computer-readable storage substrate,a random or serial access memory array or device, or a combination ofone or more of them. Moreover, while a computer storage medium is not apropagated signal, a computer storage medium can be a source ordestination of computer program instructions encoded in an artificiallygenerated propagated signal. The computer storage medium can also be, orbe included in, one or more separate physical components or media (e.g.,multiple CDs, disks, or other storage devices).

The term “data processing apparatus” encompasses all kinds of apparatus,devices, and machines for processing data, including by way of example aprogrammable processor, a computer, a system on a chip, or multipleones, or combinations, of the foregoing. The apparatus can includespecial purpose logic circuitry, e.g., an FPGA (field programmable gatearray) or an ASIC (application specific integrated circuit). Theapparatus can also include, in addition to hardware, code that createsan execution environment for the computer program in question, e.g.,code that constitutes processor firmware, a protocol stack, a databasemanagement system, an operating system, a cross-platform runtimeenvironment, a virtual machine, or a combination of one or more of them.The apparatus and execution environment can realize various differentcomputing model infrastructures, such as web services, distributedcomputing and grid computing infrastructures.

A computer program (also known as a program, software, softwareapplication, script, or code) can be written in any form of programminglanguage, including compiled or interpreted languages, declarative orprocedural languages. A computer program may, but need not, correspondto a file in a file system. A program can be stored in a portion of afile that holds other programs or data (e.g., one or more scripts storedin a markup language document), in a single file dedicated to theprogram in question, or in multiple coordinated files (e.g., files thatstore one or more modules, sub programs, or portions of code). Acomputer program can be deployed to be executed on one computer or onmultiple computers that are located at one site or distributed acrossmultiple sites and interconnected by a communication network.

Some of the processes and logic flows described in this specificationcan be performed by one or more programmable processors executing one ormore computer programs to perform actions by operating on input data andgenerating output. The processes and logic flows can also be performedby, and apparatus can also be implemented as, special purpose logiccircuitry, e.g., an FPGA (field programmable gate array) or an ASIC(application specific integrated circuit).

Processors suitable for the execution of a computer program include, byway of example, both general and special purpose microprocessors, andprocessors of any kind of digital computer. Generally, a processor willreceive instructions and data from a read only memory or a random accessmemory or both. A computer includes a processor for performing actionsin accordance with instructions and one or more memory devices forstoring instructions and data. A computer may also include, or beoperatively coupled to receive data from or transfer data to, or both,one or more mass storage devices for storing data, e.g., magnetic,magneto optical disks, or optical disks. However, a computer need nothave such devices. Devices suitable for storing computer programinstructions and data include all forms of non-volatile memory, mediaand memory devices, including by way of example semiconductor memorydevices (e.g., EPROM, EEPROM, flash memory devices, and others),magnetic disks (e.g., internal hard disks, removable disks, and others),magneto optical disks, and CD ROM and DVD-ROM disks. The processor andthe memory can be supplemented by, or incorporated in, special purposelogic circuitry.

To provide for interaction with a user, operations can be implemented ona computer having a display device (e.g., a monitor, or another type ofdisplay device) for displaying information to the user and a keyboardand a pointing device (e.g., a mouse, a trackball, a tablet, a touchsensitive screen, or another type of pointing device) by which the usercan provide input to the computer. Other kinds of devices can be used toprovide for interaction with a user as well; for example, feedbackprovided to the user can be any form of sensory feedback, e.g., visualfeedback, auditory feedback, or tactile feedback; and input from theuser can be received in any form, including acoustic, speech, or tactileinput. In addition, a computer can interact with a user by sendingdocuments to and receiving documents from a device that is used by theuser; for example, by sending web pages to a web browser on a user'sclient device in response to requests received from the web browser.

A computer system may include a single computing device, or multiplecomputers that operate in proximity or generally remote from each otherand typically interact through a communication network. Examples ofcommunication networks include a local area network (“LAN”) and a widearea network (“WAN”), an inter-network (e.g., the Internet), a networkcomprising a satellite link, and peer-to-peer networks (e.g., ad hocpeer-to-peer networks). A relationship of client and server may arise byvirtue of computer programs running on the respective computers andhaving a client-server relationship to each other.

FIG. 30 shows an example computer system 3000 that includes a processor3010, a memory 3020, a storage device 3030 and an input/output device3040. Each of the components 3010, 3020, 3030 and 3040 can beinterconnected, for example, by a system bus 3050. The processor 3010 iscapable of processing instructions for execution within the system 3000.In some implementations, the processor 3010 is a single-threadedprocessor, a multi-threaded processor, or another type of processor. Theprocessor 3010 is capable of processing instructions stored in thememory 3020 or on the storage device 3030. The memory 3020 and thestorage device 3030 can store information within the system 3000.

The input/output device 3040 provides input/output operations for thesystem 3000. In some implementations, the input/output device 3040 caninclude one or more of a network interface device, e.g., an Ethernetcard, a serial communication device, e.g., an RS-232 port, and/or awireless interface device, e.g., an 802.11 card, a 3G wireless modem, a4G wireless modem, etc. In some implementations, the input/output devicecan include driver devices configured to receive input data and sendoutput data to other input/output devices, e.g., keyboard, printer anddisplay devices 3060. In some implementations, mobile computing devices,mobile communication devices, and other devices can be used.

While this specification contains many details, these should not beconstrued as limitations on the scope of what may be claimed, but ratheras descriptions of features specific to particular examples. Certainfeatures that are described in this specification in the context ofseparate implementations can also be combined. Conversely, variousfeatures that are described in the context of a single implementationcan also be implemented in multiple embodiments separately or in anysuitable subcombination.

A number of implementations have been described. Nevertheless, it willbe understood that various modifications may be made without departingfrom the spirit and scope of the invention. Accordingly, otherimplementations are within the scope of the following claims.

1. A system for molding a photocurable material into a planar object,the system comprising: a first mold structure comprising a first moldsurface, the first mold surface comprising a planar area extending in afirst plane; a second mold structure comprising a second mold surfacecomprising a planar area extending in a second plane, wherein, at thecorresponding planar area, at least one of the first mold structure orthe second mold structure is substantially transparent to radiation atone or more wavelengths suitable for photocuring the photocurablematerial; and one or more protrusions disposed along at least one of thefirst mold surface or the second mold surface, wherein, duringoperation, the system is configured to: position the first and secondmold structures such that: the first and second mold surfaces face eachother with the one or more protrusions contacting the opposite moldsurface, the first plane is parallel to the second plane, and a volumehaving a total thickness variation (TTV) of 500 nm or less is definedbetween the first and second mold surfaces adjacent the correspondingplanar areas, receive the photocurable material in the volume, anddirect radiation at the one or more wavelengths into the volume.
 2. Thesystem of claim 1, wherein each of the first mold structure and thesecond mold structure has a thickness greater than 1 mm.
 3. The systemof claim 1, wherein each of the first mold structure and the second moldstructure has a thickness between 1 mm and 50 mm.
 4. The system of claim1, wherein each of the first mold structure and the second moldstructure has a diameter greater than 3 inches.
 5. The system of claim1, wherein the system further comprises one or more recesses definedalong at least one of the first mold surface or the second mold surface.6. The system of claim 5, wherein, during operation, at least some ofthe one or more protrusions is in alignment with the at least some ofthe one or more recesses, such that when the system positions the firstand second mold structures so that the first and second mold surfacesface each other with the one or more protrusions contacting the oppositesurface, at least some of the one or more protrusions insert, at leastpartially, into at least some of the recesses.
 7. The system of claim 6,wherein at least some of the one or more protrusions are disposed alonga periphery of the first mold surface.
 8. The system of claim 6, whereinat least some of the one or more protrusions are disposed along aninterior of the first mold surface.
 9. The system of claim 7, wherein atleast some of the one or more recesses protrusions are disposed along aperiphery of the second mold surface.
 10. The system of claim 7, whereinat least some of the one or more recesses protrusions are disposed alongan interior of the second mold surface.
 11. The system of claim 1,wherein at least some of the one or more protrusions have asubstantially rectangular cross-section.
 12. The system of claim 11,wherein at least some of the one or more protrusions having thesubstantially rectangular cross-section further comprises a respectivesubstantially hemispherical distal end.
 13. The system of claim 11,wherein at least some of the one or more protrusions having thesubstantially rectangular cross-section further comprises one or morerounded corners.
 14. The system of claim 1, wherein at least some of theone or more protrusions have a substantially triangular cross-section.15. The system of claim 14, wherein at least some of the one or moreprotrusions having the substantially triangular cross-section furthercomprises one or more rounded corners.
 16. The system of claim 5,wherein at least some of the one or more recesses have a substantiallyrectangular cross-section.
 17. The system of claim 16, wherein at leastsome of the one or more recesses having the substantially rectangularcross-section further comprises one or more rounded corners.
 18. Thesystem of claim 5, wherein at least some of the one or more recesseshave a substantially triangular cross-section.
 19. The system of claim18, wherein at least some of the one or more recesses having thesubstantially triangular cross-section further comprises one or morerounded corners.
 20. The system of claim 1, wherein at least some of theone or more protrusions are integral with least one of the first moldsurface or the second mold surface.
 21. The system of claim 1, whereinat least some of the one or more protrusions are detachable from thefirst mold surface or the second mold surface.
 22. The system of claim1, further comprising a light assembly configured to emit one or morewavelengths of radiation suitable for photocuring the photocurablematerial.
 23. The system of claim 1, wherein the first and second moldsurfaces are polished surfaces.
 24. The system of claim 1, wherein,during operation, the system is configured to position the first andsecond mold structures such that the volume defined between the firstand second mold surfaces adjacent the corresponding planar areas has atotal thickness variation (TTV) of 100 nm or less.
 25. The system ofclaim 1, wherein each of the one or more protrusions has a totalthickness variation of 100 nm or less.
 26. The system of claim 5,wherein each of the one or more recesses has a total thickness variationof 100 nm or less.
 27. The system of claim 1, wherein, during operation,the system is configured to position the first and second moldstructures such that the volume defined between the first and secondmold surfaces adjacent the corresponding planar areas has a thicknessbetween 20 μm and 2 mm.
 28. The system of claim 1, wherein, duringoperation, the system is configured to direct heat into the volume. 29.The system of claim 28, wherein, during operation, the system isconfigured to direct heat into the volume through the first moldsurface.
 30. The system of claim 29, wherein, during operation, thesystem is configured to direct heat into the volume through the secondmold surface.
 31. The system of claim 1, wherein, during operation, thesystem is configured to direct the one or more wavelengths of radiationinto the volume through the first mold surface.
 32. The system of claim1, wherein, during operation, the system is configured to direct the oneor more wavelengths of radiation into the volume through the second moldsurface.
 33. A method of forming a waveguide part having a predeterminedshape, the method comprising: providing a first mold portion having afirst surface comprising a discrete, continuous first area correspondingto the predetermined shape of the waveguide part, the first area beingbounded by an edge region having a different surface chemistry and/orsurface structure than the first area; providing a second mold portionhaving a second surface comprising a discrete, continuous second areacorresponding to the predetermined shape of the waveguide part, thesecond area being bounded by an edge region having a different surfacechemistry and/or surface structure than the second area; dispensing ametered amount of a photocurable material into a space adjacent thefirst area of the first mold portion; arranging the first and secondsurfaces opposite each other with the first and second areas beingregistered with respect to each other; adjusting a relative separationbetween the first surface and the second surface so that thephotocurable material fills a space between first and second areas ofthe first and second surfaces, respectively, having the predeterminedshape, the different surface chemistry and/or surface structure betweenthe first and second areas and their corresponding edge regionspreventing flow of the photocurable material beyond the edge regions;irradiating the photocurable material in the space with radiationsuitable for photocuring the photocurable material to form a cured filmin the shape of the waveguide part; and separating the cured film fromthe first and second mold portions to provide the waveguide part.34.-47. (canceled)
 48. A mold system for forming a waveguide part havinga predetermined shape, the mold comprising: a first mold portion havinga first surface comprising a discrete, continuous first areacorresponding to the predetermined shape of the waveguide part, thefirst area being bounded by an edge region; a second mold portion havinga second surface comprising a discrete, continuous second areacorresponding to the predetermined shape of the waveguide part, thesecond area being bounded by an edge region having a different surfacechemistry and/or surface structure than the second area; one or morespacers on the first and/or second surfaces located outside of the firstand second areas, respectively; and one or more fiducial markings on thefirst and/or second surfaces located outside of the first and secondareas, respectively, wherein the edge region of the first and secondsurfaces each have a different surface chemistry and/or surfacestructure than the first area and second areas, respectively, such thata surface energy of a photocurable material for forming the waveguidepart is different at the edge regions compared to the first and secondareas, respectively. 49.-57. (canceled)
 58. A method of forming awaveguide film, the method comprising: dispensing a photocurablematerial into a space between a first mold portion and a second moldportion opposite the first mold portion; adjusting a relative separationbetween a surface of the first mold portion with respect to a surface ofthe second mold portion opposing the surface of the first mold portion;irradiating the photocurable material in the space with radiationsuitable for photocuring the photocurable material to form a curedwaveguide film; and concurrent to irradiating the photocurable material,performing at least one of: varying the relative separation between thesurface of the first mold portion and the surface of the second moldportion; and varying an intensity of the radiation irradiating thephotocurable material. 59.-78. (canceled)